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I've heard of a few rotten ones being broken for spares, but I've yet to see any car go from solid to rotten in a few months. Unless the 'solid' appearance was just that...an appearance which was hiding the rot fairly well.
I'd bet you're right. Come to think of it there was some traces on 'pon around the arch - it would have been some amount of it hide this though. The boot floor problems were hidden by the spare wheel.
That coupe is lovely - looks like a Toyota 2000, which is no bad thing!