I've noticed that on school chrome books (Atleast at hall county schools) if you change your password it doesn't affect chromebooks that are already signed in. I can't really show you system logs as the school administrators lock down the chromebooks and since im a student i can't really do anything.
Example:
1. I find out my friends password "insert password here"
I used to go into his account and mess with his background etc i always tell him but then he changes his password through our schools launch point portal. But if I try to login to his account on a chrome book without his account already in it wont let me with his new password but if he already is signed in i can sign in and i have full access to his FULL google account. Infact I changed his profile picture to Barack Obama and it affected it even though he changed his password.