"Federal Service to Date" required for survivor annuity payments/?

[Ana Waxer]

I recieved a 1099-R for an inheritance I got in 2023. 

It is prompting me for "Federal Service to date"

what does this mean?

Is it asking for the total number of years the person worked for the federal government?

Is it asking for the starting date?

I only know the retirement year (1985) I wasnt very close with the person.

Do I need to be 100% accurate?