Drawing room

Spoilers for a puzzle below:

!Ok so I got the code to the safe is 0415 because of count small gaits, there's 15 of the guy. But why is is April? I just brute forced the month since I figured there's only 12 options but I can't for the life of me see where I was supposed to get that from otherwise lol. Is there an actual reason it's 04 or are you supposed to just try all options?!<

Same with the >!May8 code!< in the underground gear room actually, >!I assumed it was a date with 3 letters but is there an actual reason I would have known that without guessing?!<