I would look at a credit report for Citi cards opened in 2020, to see the months in which they were opened. If there is more than one, use the latest one, and add four months to estimate when you might have received the bonus.
I would also look for emails with the search term "Citi Premier". For example, I have an email with this Subject: You've activated your Citi PremierSM Mastercard®
I already checked the credit reports...and gave the open/close dates to Citi of the 2 closed accounts from 2021 and 2022....they cannot pull up closed account info that old.
I don't save emails, either. Grr...
I even searched my old posts here to see if I posted about it!
EDIT: FOUND IT doing a different type of search on FT of my old posts!
Woohoo!!!!
Citi's maximum credit they will extend relative to income