Turns out, Castorland also uses the same dies for 500 piece puzzles, but in this case, the puzzles fit on each other so that the other image needs to be upside down. That was something I hadn’t considered. The two jigsaws I used were Sunset Harbour and The Stony Bridge.
These work a bit better than the previous ones, but nothing spectacular yet. The puzzle mashup artist, Tim Klein, did say that he preferred older puzzles because new ones are so busy and full of detail. I think he’s right, this mashup thing would probably work better with less stuff in the images, to begin with. I kind of like the sunshade landing in the garden, though.