Where is this patch you are talking about?
p.s. but not worth it, I wouldn't use the two extra ones.
Ah. It is probably DLC that I am not entitled to, so I can't see it.
GOG patches are not cumulative (talking about the pre-Galaxy days) so they always check that the version of the game is the correct one, just prior to the patch you want to install. If they don't match expectation, then they throw the compatibility error msg that you found and they refuse to apply.
That said, DLC should not be so finicky about what you can apply it to. I think GOG made a mistake and you should open a support ticket.