There are two layers to encrypt the /data partition, one that is built into the hardware, and one is the password or pin you enter, and they are supposed to work together/be combined. So it should be possible theoretically that the encryption is in place without your password, by only using the hardware key.
I also experienced that already a few times during updates or OS changes that encryption seemed to be in place though I didn’t get asked for my pw, which is not the behaviour I expect or want to have, as it makes my data easier accessible.
I use the app snooperstopper to have a different password than for the lock screen, and resetting the password there solves the problem and I get asked again for my password on start up.