Hi everyone! I am a student who is very new to STATA and much appreciated if someone could help with the below questions.

I was asked to design an empirical strategy to see whether the share of printing in Venice decline after 1498.

I have 1000 random samples of published material including the cities where they were printed and the print year, during 1475 - 1650. In other words, the two variables are Venice (dummy variable, equals to 1 if the material is printed in Venice) and t (the year of print).

I have used the below codes to generate the variable for the share of printing in Venice per year:

egen venicet = sum(venice), by(t)
gen sample =1
egen total = sum(sample), by(t)
drop sample
gen share = venicet/total

However, this gives me multiple same observations for one year (for example in the table below), and I am not sure how I can then line the change of share over years (keep only one share observation per year), and to create the empirical strategy to see whether the share of printing in Venice decline after 1498. Please give me some suggestions on this, many thanks!!!
Venice t share
1 1479 0.25
0 1479 0.25
0 1479 0.25
0 1479 0.25
1 1484 0.2
1 1484 0.2
0 1484 0.2
0 1484 0.2
0 1484 0.2