Tudor Sub Marine Nationale - help appreciated

Many thanks @Dre, that is quite an interesting observation, and something I never thought to consider because it seems extremely speculative. I assume you are saying that the scratches should be visible within the sunken parts of the engraved letters and numbers. Honestly, I'm not sure that's always the case. I don't want to come off as being defensive, but I also don't want to jump to incorrect conclusions about the engraving being fake, since two people have indicated that the serial number is in the correct 5-digit batch for an MN piece.

When I think about how light parallel scratches like these could occur, it's not clear to me whether or not they should continue through the engraving or not; I can imagine both scenarios. For example, scratches due to grit under a NATO strap or a rough cloth of some type would probably not visibly continue through the bottom of an engraving. Scratches due to a steel tool could continue through an engraving if a lot of pressure were used, but I'm not sure I would expect multiple parallel scratches like these from a tool. There are a lot of light scratches and damage on the case-back, and I'm really not sure of the source.

I've tried to blow up that part of the photo to get a better look. It seems that one scratch does continue through the bottom of the "8", but it's quite hard to be sure. There also seems to be a vertical line connecting to the scratch on the left side of the "N", but again I'm not totally sure because it could be a tool mark. To be honest, as a scientist, I feel that this type of forensic analysis based on scratches is overly speculative. It's unclear whether the scratches should continue or not. And it's also very hard to determine whether or not they continue.

I'd be very surprised to see a light scratch continue though a deep engraving. It would, as @Dan S says, have to been applied with some force in order for that to happen and in that case the scratch would be deeper.

In fact, as I am typing this, I realise that I'm currently wearing an Omega "Dirty Dozen" and I take it off and have a look at the caseback. None of the light scratches evident there make any sort of mark on the engravings - and that is most certainly not a faked caseback.

It is not extremely speculative way to see in vintage sports Rolex/Tudor watches, a "super" dealer taught me this. But I suppose I just like to keep it simple for something that is commonly faked and carries a steep premium, just walk away when there is one thing (where the value lies most in this case) looks wrong. So I probably made that "I'd avoid that if I were you" comment too soon.

I know that feeling when you get offered privately, locally, or by someone that you know on what looks like to be a great watch. Only to turns out that there's something wrong with the watch, but you still trying to prove it to be ok, because you want it to be the real deal. Happened to me twice recently on a couple of "grail" watches on what I thought were the real deal initially.

These MN watches are highly desirable, if it's the real deal without any doubt on the engraving, you should already have people sending you DMs offering to purchase the watch. You should inspect the engraving properly in person with a good loupe. I do hope it's a real deal for you tho, so good luck.

Very good points, and I really don't want to "prove it to be ok", but I also don't want to be overly conservative if the Tudor MN experts think it looks OK. To be perfectly honest, I'm not particularly attracted to Tudor as a brand; I've never even considered purchasing one before. So this is no "grail" for me. It's just an opportunity that arose, and the price would have to be right for a piece without provenance. I'm not going to buy this at an "MN" price. If I'm convinced that the case-back is faked, then I'm not going to buy it at all.

Very good way to think about this. I just checked some sales, and it looks like a civilian Mercedes hand 1980s Tudor sub would sell for roughly $5k usd, so that seems like a reasonable starting point for this one, especially since the insert appears to be a replacement.

Who is Jason? Sorry, I don't know everyone by name.

Edit: I did some searching through the forum archives and figured out that Jason refers to @964RS. He signed his name to a post in 2016.

Does anyone know how to contact the person who owns the Toulon service ledgers? Feel free to send me a message if you don't want to post the information publicly.

Many thanks to everyone who has responded to me here, on MWR, and by email. Regardless of whether you gave thumbs-up or thumbs-down, you pushed me to do more research and learn about the watch.

Ultimately, despite the lack of written documentation, I came to believe that the watch was legit with a good level of certainty, based on opinions from several experts and especially some specific details that Ross Povey (TudorCollector.com) was able to provide by a remarkable coincidence. The owner and I worked out a mutually agreeable two watch trade, where I acquired the Tudor and a Titus Calypsomatic 7986.

The bezel insert isn't original, so I'd like to figure out what type of insert that would be correct for an early 1980s Tudor Sub. Are they the same as Rolex inserts, or were the Tudor inserts unique? I see Rolex inserts for sale now and then, and they have names like Mk III, Mk IV, etc. Is that what I'm looking for?