We get asked this one quite a lot. Originality of a watch is often a concern for collectors, who are looking for pristine unmolested examples, but it's also asked by lots of people new to vintage watches are really more concerned that the watch that they are buying is not a collection of disparate parts from a bucket of spares.
Let's tackle some of the simple stuff first.
- Acrylic glasses (crystals), crowns (winding button), stems and straps are all wear items. These are the parts of the watch that take the most abuse when a watch is worn. Crystals get scuffed up against door posts, brick walls, even wearing at your desk for a few days is enough to put a noticeable mark in the soft acrylic of a typical vintage watch glass. Crowns get turned 10-15 times, every day for 40 years, so the little ridges milled into the perimeter are going to wear out. If you are unlucky enough to knock your watch heavily on the crown, you might also break a stem. Leather straps become brittle and stitching rots, leading to failure within a few years of heavy use.
So when you ask us if a 70 year old watch is completely original, unless, it's been worn less than a handful of times and spent most of it's life in the dark in a dehumidified room, it's more than likely to have had replacements of one or more of the above. This is normal. You wouldn't buy a 1965 Mercedes that had never had any replacement parts, (at least I wouldn't ) so we can surmise that service parts are OK to change without harming the originality of the watch. It's often possible to replace a vintage watch crown for example with a new replacement from the same manufacturer, although the routes to genuine OE spares for independent retailers are being increasingly closed down.
- Dials. Original dials are always sought after, but inevitably on a 50-70 year old watch you are going to see some level of deterioration. This is normal. How much deterioration you can personally live with, often dictates the decision to have the dial refurbished. A refurbished or restored dial is the original dial but the original printing and finish is completely stripped, repainted and reprinted. This can offend some collectors but 14 years of watch trading have taught me that watches with clean dials always sell better than those with the roadworn look. There are exceptions of course for special pieces which should never be touched, ever. A pristine original dial will always fetch the best price though.
-Hands. Some collectors can get very animated about the originality of watch hands. Often watch hands will corrode or even break in servicing, for really old pieces, and there's no issue in my view in replacing hands from another watch or new old stock parts as long as they are the correct hands for the model and age of watch. There are of course those that adopt an 'anything that fits' attitude and I've even seen watches trading for high prices where the minute hand is a completely different design to the hour hand. They should definitely be avoided.
- Movements. It's actually quite difficult to put a movement from one watch into another unless the case was designed for it. It's pretty similar to trying to put a Ford engine in a Ferrari, it just won't fit. Cases are specifically designed to fit a particular dial and movement combination. It is entirely possible to swap parts from the same calibre movement. So if an escape wheel in a calibre 601 Omega breaks a pivot, you can take the same part from another cal. 601 and fix the broken watch. Furthermore, it's impossible to tell that this has been done. The parts are made in the same factory, the repairer has just done what Omega themselves did 50+ years ago when they made the watch. This isn't a problem, originality is not harmed, it's exactly the same watch it always was. What would be concerning is if you could take for example a balance wheel from an ETA and put it in a Rolex. Thankfully this isn't possible, it wouldn't fit and would be obvious to the trained eye as well. This would of course lower the intrinsic quality of the piece. Some generic parts are made of course but these are generally confined to service parts such as setting lever springs, stems, generic clamps etc.
More legitimate concerns would be replacing similar parts to get a completely worn out movement running again or nasty bodges such as glued in jewels to overcome missing incabloc springs, fitting a crystal that is completely wrong/ inappropriate for the case or polishing off worn gold plating to give a watch the appearance of shiny new stainless steel indicate a watch of dubious origin. Beware of the classic, pristine restored dial with dirty worn out movement often with missing case screws/ clamps. Such watches will never run properly.
So in summary, most concerns about parts are often not something to worry about, some are impossible to even to detect that they have been changed. In collecting, we tend to look at the balance of the piece, if it is overwhelmingly genuine with perhaps a replacement generic crown, we shouldn't dismiss an otherwise good watch. The chance to change a crown for a genuine item at a later stage is always possible as is fitting a brand new strap from the original manufacturer.