A bit of an update, I managed to find the keys, but there seems to be an issue. The master key is single use, but there are multiple doors that use it.
Viewing post in Soggy Horror Spoopfest '24 Hotfix comments
Yup, That issue is known and is not intentional. the doors that use that key need a flag to not consume the key on use. as is with some items being mislabeled on the text prompt when you pick them up. quite a few have the diaper pack prompt and I haven't prioritize it yet as I want to make sure the final area plays well and isn't needlessly cruel since Thorn is already really pushing it.
The other known issue is there are a few objects that need flags corrected for the save system to work as built. That will likely be ironed out a bit after Halloween since it has always been extremely fickle.