Gmail import incomplete - how to fix?

[AGB]

Hi Everyone,

I have the following problem: I wanted to transfer all old email from one gmail account (gmail1) to another (gmail2), in view of keeping only newly incoming mail in gmail1. I must have used the instructions here: https://support.google.com/mail/answer/21289?hl=en&sjid=13230923034771854690-EU, and having stopped the importing after a few days. Comparing content between gmail1 and gmail2, I now see that a lot of emails have indeed been imported in gmail2, but not all. I cannot find a rule for which emails are missing, and I also don't have a way to highlight which of the old emails have not been imported. 

Is there anything I can do to complete the old email import from gmail1 to gmail2 (much like running rsync between two computer folders, where only the differences would be transferred)?

I would be SO grateful for help sorting this out!

Thanks,

Alina