@ciane The problem with using "Save As" instead of "Save" for the Isla Paradiso game is, when I did that, one of the folders it created was one with a .bad extension, which suggests that save game is also corrupted somehow, and if that's the case I feel it would be risky to be using a potentially corrupted save game.
@igazor In all 3 downloads, the first folder was named IPonlyRdy.sims3. In the 3rd download, when I tested out "Save As", the split-off game was called Isla Paradiso.sims3.
I will test out adding a number, though I don't understand how that would fix an error. Also @Mmdrgntobldrgn gave me an idea; I have yet to install SaveCleaner, do you think that may help?