Hello, I am playing on the last version, I was able to get up to 101% completion, with all secrets and skins found.
The problem is that the map is saying that Stages 00, 61 and 52 are incomplete. I do think that Stage 61 might have a secret exit because it leads to nothing, but the other two I am not so sure, I tried using sneak after killing the snake on 52 but it didn't change anything.
I can't seem to find a way to find the missing doors or entrances.
I was wondering if this is a bug or if those areas require entering from another area, but since those three places are the only white places, I don't think they can connect with each other based on the position on the map.
The game is great, thanks for making it, loved the references, I hope someone makes a guide one day since it's very hard to find information on how to beat or find secrets.