Longines serial number to production year websites: Doomed to fail?

Hey everyone,

I've got two vintage Longineses for which I received extract from the archives. One of them, a Longines invoiced on 1918, has a serial number (3,3xx,xxx) referring to the production year of 1915, which is quite ok, according to the websites below:

http://www.pocketwatchrepair.com/histories/longines.php

https://millenarywatches.com/longines-serial-number/

https://serial-number-decoder.co.uk/longines/longines.htm

However, when I got the same.service for my other Longines yesterday, I was totally surprised! The serial number of my watch, starting with 13,8xx,xxx was invoiced in 1962 instead of 1966, as the websites above would suggest.

In the discussion for 1918 watch, @Syrte has rightfully voiced his concerns about the accuracy and background of the websites above. While sharing the same concerns, I've so far observed that they were somehow accurate but the case with 1962 watch made me more suspicious about them.

All in all, I believe that there could be two possibilities: either the websites aren't accurate or Longines sometimes invoiced watches before they were produced. To me, the latter is a bit ridiculous given the difference of 4 years in my case.

What do you guys think?

Edit: typo

To be honest and in my humble opinion I don’t think it really matters. For myself I only use those websites to provide a preliminary estimate to roughly date the watch.

Thankfully Longines has an amazing archive and history department, they are extremely fast at providing free extracts of archives, and that’s the info I look at once they have replied.

I’ve always wondered where and how those other numbers were obtained, but I don’t think it’s such a big deal.

Exactly, that's also how I see them. So far, they were pretty accurate for the watches I looked up but the last attempt has been a huge fail for the websites... I'll keep sticking to extracts, as well.