I agree with Jeff, though I think there are times when design intent didn't quite match the practicalities of production, and they used whatever was at hand and in stock. We would probably call Heuer wristwatch volumes a boutique operation today, with all that entails regarding keeping stock, ordering and not so strict adherence to design. So some of the 'mismatched' hands possibly did leave the factory like that rather than being later replacements.

It's right that it gives us pause for thought rather than always accepting it prima facie. There are definitely some more recently assembled watches out there, so best not to write off every discrepancy as factory practice.