The mechanical watches are not open source at all - most (all?) of them do not come with engineering drawings nor with list of materials.

Even if you have a watch in front of you, it does not mean you can create a copy of it without a lot of work - you need to measure every gear, guess the materials used (how stiff should this spring be?), and re-draw mainplate and dial.

Compare to things like old electronics, which came with full schematics, service manual and sometimes even debugging guide.