Hello everyone,
I am working with panel data, and I would like to ask you again for help.
I would like to replace missing values in master data with values from using data, based on time criterion.

Master file Merging.dta
Code:
clear
input double(crsp_fundno crsp_portno) float mofd
1788 . 405
1788 . 406
1788 . 407
1788 . 408
1788 . 409
1788 . 410
1788 . 411
1788 . 412
1788 . 413
1788 . 414
1788 . 415
1788 . 416
1788 . 417
1788 . 418
1788 . 419
1788 . 420
1788 . 421
1788 . 422
1788 . 423
1788 . 424
1788 . 425
.... . ...
1788 . 600
1788 . 601
1788 . 602
1788 . 603
1788 . 604
1788 . 605
1788 . 606
end
Using file FundnotoPortno.dta

Code:
clear
input double(crsp_fundno crsp_portno) float(begmofd endmofd)
1788 1009555 582 604
1788 1023119 605 740
2118 1028804 611 740
end
Begmofd - starting month
Endmofd - ending month
As in the example above of the using file, the data shows that a different crsp_portno can apply to the same crsp_fundno, but over different time period. Some crsp_fundnos can have only one range.
The example of the master file is an extreme one, as the the earliest time record is 405, which is outside of the 582-604 month range. Although 405 is lower than 582, I still would like to replace those missing crsp_portno values from master file with the crsp_portno from the using file, using the lower range.
May I kindly ask you to tell me how should I perform it? I have never before run such a command, and therefore it seems quite complex for me.

Thank you very much for any help or advice!

Best,
Rafał