Thanks for your help! But I think it's better to play from the beginning again. I actually didn't feel like playing from the beginning anymore because it takes extremely long. And thanks for pointing out that you should play the Marcus route last in episode 2, because that's a perfect transition to episode 3, since you're free again.The gallery is unlocked by the corresponding entries in the persistent file (it's in the "saves" folder), not the save itself, even if it's a developer save file. So if your old persistent file is no longer available, you will need a new persistent file which will contain the appropriate entries for your playing style. (by "style" I mean different ep2 playthroughs, which can vary depending on the preferences of the individual player).
Theoretically, you could try searching for old versions of the scrappy mod that worked for Ep2 v16, and thus open those scenes that you have already passed before. Also, you can ask here for a persistence file that will work for you.