I'm glad you enjoyed the game! In the memories section of the current build (v0.3.1.1), all of the unlockables are shown by default and if you did not encounter the scene yet then you wouldn't be able to replay them. So if you can replay all of the scenes in memories mode then you have successfully unlocked all of them.
In the upcoming version, I overhauled the memories page and separated all of the unlockables for each day. Additionally there will be "Locked" indicator in the next release which will let you know if there are any scenes left that you have not encountered yet.
My plan is to have the dorm mother change each day since they are volunteers after all, but there is a good chance they will get a spanking in later days.