I´m using the command "append" to add four dta files. Each dta. file constains data on a quarter of the year 2020. I already check each dta. file and I don´t find any problem. However, when I use the command "append" and I add the last file (with data for the last quarter of the year) an error appears: The variable "country" and the variable country_ (created with the command "encode") don´t mach. The error appears only in the data of the last file (last quarter of the year).
Can you help me with this problem? I don´t understand what it can be.
Below I send the example of my data (with the error included).
Thank you in advance.


Code:
* Example generated by -dataex-. To install: ssc install dataex
clear
input str22 country double no2_median float(date yearweek) long country_
"Argentina"               7.4 21913 3119  3
"Austria"                15.6 21913 3119  5
"Belgium"                15.1 21913 3119  8
"Bolivia"                 6.7 21913 3119  9
"Bosnia and Herzegovina"  6.9 21913 3119 10
"Brazil"                  7.8 21913 3119 11
"Canada"                  5.2 21913 3119 13
"Chile"                  13.2 21913 3119 14
"China"                  22.4 21913 3119 15
"Colombia"                6.9 21913 3119 16
"Croatia"                24.3 21913 3119 18
"Cyprus"                 11.5 21913 3119 20
"Czech Republic"         12.9 21913 3119 21
"Denmark"                 9.1 21913 3119 22
"Estonia"                 2.5 21913 3119 25
"Finland"                 5.6 21913 3119 27
"France"                 27.6 21913 3119 28
"Georgia"                14.2 21913 3119 29
"Germany"                16.5 21913 3119 30
"Greece"                    6 21913 3119 32
"Hong Kong"              21.4 21913 3119 35
"Hungary"                18.4 21913 3119 36
"Iceland"                 5.9 21913 3119 37
"India"                  20.8 21913 3119 38
"Iran"                     56 21913 3119 40
"Ireland"                 6.4 21913 3119 42
"Israel"                 12.5 21913 3119 43
"Italy"                    11 21913 3119 44
"Japan"                  16.7 21913 3119 46
"Jordan"                 15.5 21913 3119 47
"Kosovo"                 11.9 21913 3119 49
"Macedonia"               4.4 21913 3119 55
"Mexico"                 15.8 21913 3119 58
"Mongolia"               11.2 21913 3119 59
"Netherlands"            21.8 21913 3119 62
"New Zealand"             1.3 21913 3119 63
"Norway"                  7.1 21913 3119 64
"Peru"                    5.6 21913 3119 66
"Poland"                  9.9 21913 3119 68
"Portugal"               17.7 21913 3119 69
"Reunion"                 2.2 21913 3119 71
"Romania"                 8.8 21913 3119 72
"Russia"                  8.1 21913 3119 73
"Serbia"                 10.8 21913 3119 75
"Slovakia"               11.5 21913 3119 77
"South Africa"            8.3 21913 3119 78
"South Korea"            32.5 21913 3119 79
"Spain"                  28.8 21913 3119 80
"Sweden"                  4.7 21913 3119 82
"Switzerland"            13.9 21913 3119 83
"Taiwan"                 15.8 21913 3119 84
"Thailand"               14.4 21913 3119 86
"Turkey"                 16.1 21913 3119 87
"United Arab Emirates"   19.2 21913 3119 91
"United Kingdom"         21.6 21913 3119 92
"United States"           9.2 21913 3119 93
"Vietnam"                   8 21913 3119 95
"Argentina"               3.7 21914 3119  3
"Austria"                10.1 21914 3119  5
"Belgium"                17.9 21914 3119  8
"Bolivia"                 7.8 21914 3119  9
"Bosnia and Herzegovina" 11.5 21914 3119 10
"Brazil"                  8.3 21914 3119 11
"Canada"                  9.4 21914 3119 13
"Chile"                    15 21914 3119 14
"China"                  19.7 21914 3119 15
"Colombia"                  7 21914 3119 16
"Croatia"                21.5 21914 3119 18
"Cyprus"                 12.5 21914 3119 20
"Czech Republic"           11 21914 3119 21
"Denmark"                 3.3 21914 3119 22
"Estonia"                 1.3 21914 3119 25
"Finland"                 4.3 21914 3119 27
"France"                 26.1 21914 3119 28
"Georgia"                13.3 21914 3119 29
"Germany"                11.5 21914 3119 30
"Greece"                  6.9 21914 3119 32
"Hong Kong"              18.5 21914 3119 35
"Hungary"                 9.8 21914 3119 36
"Iceland"                   2 21914 3119 37
"India"                  16.3 21914 3119 38
"Iran"                     55 21914 3119 40
"Ireland"                10.6 21914 3119 42
"Italy"                  19.2 21914 3119 44
"Japan"                  15.8 21914 3119 46
"Jordan"                 15.8 21914 3119 47
"Kosovo"                 18.6 21914 3119 49
"Macedonia"               8.5 21914 3119 55
"Mexico"                 19.5 21914 3119 58
"Mongolia"                 12 21914 3119 59
"Netherlands"            17.7 21914 3119 62
"New Zealand"             1.4 21914 3119 63
"Norway"                 19.6 21914 3119 64
"Peru"                      8 21914 3119 66
"Philippines"             4.6 21914 3119 67
"Poland"                  5.8 21914 3119 68
"Portugal"               13.4 21914 3119 69
"Reunion"                 1.8 21914 3119 71
"Romania"                 8.9 21914 3119 72
"Russia"                  8.7 21914 3119 73
end
format %td date
format %tw yearweek
label values country_ country_
label def country_ 3 "Argentina", modify
label def country_ 5 "Austria", modify
label def country_ 8 "Belgium", modify
label def country_ 9 "Bolivia", modify
label def country_ 10 "Bosnia and Herzegovina", modify
label def country_ 11 "Brazil", modify
label def country_ 13 "Canada", modify
label def country_ 14 "Chile", modify
label def country_ 15 "China", modify
label def country_ 16 "Colombia", modify
label def country_ 18 "Croatia", modify
label def country_ 20 "Cyprus", modify
label def country_ 21 "Czech Republic", modify
label def country_ 22 "Denmark", modify
label def country_ 25 "Estonia", modify
label def country_ 27 "Finland", modify
label def country_ 28 "France", modify
label def country_ 29 "Georgia", modify
label def country_ 30 "Germany", modify
label def country_ 32 "Greece", modify
label def country_ 35 "Hong Kong", modify
label def country_ 36 "Hungary", modify
label def country_ 37 "Iceland", modify
label def country_ 38 "India", modify
label def country_ 40 "Iran", modify
label def country_ 42 "Ireland", modify
label def country_ 43 "Israel", modify
label def country_ 44 "Italy", modify
label def country_ 46 "Japan", modify
label def country_ 47 "Jordan", modify
label def country_ 49 "Kosovo", modify
label def country_ 55 "Macedonia", modify
label def country_ 58 "Mexico", modify
label def country_ 59 "Mongolia", modify
label def country_ 62 "Netherlands", modify
label def country_ 63 "New Zealand", modify
label def country_ 64 "Norway", modify
label def country_ 66 "Peru", modify
label def country_ 67 "Philippines", modify
label def country_ 68 "Poland", modify
label def country_ 69 "Portugal", modify
label def country_ 71 "Reunion", modify
label def country_ 72 "Romania", modify
label def country_ 73 "Russia", modify
label def country_ 75 "Serbia", modify
label def country_ 77 "Slovakia", modify
label def country_ 78 "South Africa", modify
label def country_ 79 "South Korea", modify
label def country_ 80 "Spain", modify
label def country_ 82 "Sweden", modify
label def country_ 83 "Switzerland", modify
label def country_ 84 "Taiwan", modify
label def country_ 86 "Thailand", modify
label def country_ 87 "Turkey", modify
label def country_ 91 "United Arab Emirates", modify
label def country_ 92 "United Kingdom", modify
label def country_ 93 "United States", modify
label def country_ 95 "Vietnam", modify