That's true. What are the chances of someone just happening to need your parts and having the parts you need?
Broadly speaking, although OBM etc used to list potential swaps, do such swaps ever happen in reality?
I'm sure a 1969 Tiger 100 head could be swapped for a 1971 head, but obscure parts from long gone models must be next to impossible.
Anyway, I have a 1912 FN rear wheel spindle and I need a 1936 Super X tyre pump. Any takers...