But don't take it from me -- I would call them and ask what the difference is. It's their website. And please let me know what they say.
They said "NO DIFFERENCE". It is simply some MFGs (both gun and ammo) don't like to put "WIN" on their stuff.
Now, the NATO 762 can fire out of either but you should be careful of firing commercial .308 out of a Military rifle due to head space in the chamber.