Thank you! I'm glad you liked it!
You should be able to click on and learn about the art from the moment that the cat joins you and tells you to look around at the decor. It doesn't tell the player directly but it should always replace the help button when the art is on screen as long as the cat is with you.
The dialogue where the cat reminds you after the mirror was just to let the player know that you could click on the Shalott paintings again to learn about them. I was worried that people would think that you weren't able to do that since the cat read the poem about them. There is no information change about any of the other paintings.
As for why they were in the sealed room, I just didn't have any other place to put them which is why there's a warning to look at them before sealing it. Hope that helps!