Why do Omega Nato's come with two sets of spring bars, with different lengths?

No, it was definitely the black/grey nylon NATO that had a "21mm" sticker on the packet. Of course, it doesn't mean that there wasn't a 21.5mm strap in the packet if they haven't changed the design as you say. Thanks for confirming. It may be that the .5mm part was worn away or it was a replacement packet. Seems a shame though, as for the money I'd prefer an exact fit.

Yes, I have a "golden brown" (tan) leather Omega NATO which is marked 21mm and is 21mm exactly. Very comfy strap!

You've got to be lucky who you buy from. The OMEGA boutique in Bond St., I've bought from a few times, and I always get told 'we don't stock any spring bars' when I've asked if they have any. I call bull on that, There is no way that they don't hold ANY spring bars in a shop that sells only watches, What really, no spares in case you need them? Needless to say, I was far from impressed, and I wouldn't buy from them again when they're charging me well over £140 GB for a bit of nylon or whatever it is. I only bought from them again for convenience. I've always had to order bars from dealers if I want original OMEGA. And direct from OMEGA was a joke too, they consider it a 'part', as in we don't sell parts to the public. Like I was asking for a crown and bezel.

You're right about the oversight/mistake, I think. When I purchased my 2021 model 300MC, I found that one piece of the strap didn't match the other in daylight - although it looked fine in the blazing boutique lighting! The OB manager was very good about it and offered a replacement or an equivalent swap and I went for the golden brown leather 21mm NATO.

No spring bars were provided, however and I've chosen to use 1.5mm diameter aftermarket straight spring bars which make the gap to the case better than the originals. I wish I had thought to ask for the curved bars at the time, but it was a few weeks ago now....

So would all my 20mm NATOs for my 42mm POs, fit the 19mm 8800 if I bought one of them?

You have to ask them about it, they usually don’t hand them out just because, they retail for like 4-5 bucks but I must have gotten like 6 pairs gratis just by chatting them up and asking casually lololol OB Workers need a little love sometimes hahaha