The pre D3V version of the FK aka FK1 aka OGFK were hardened at a slightly higher number on the Rockwell scale. Even Nathan's "plain" 3V predating the Delta-HT protocol was heat treated at levels above and beyond the industry standard HT for 3V steel.
Sometimes you can look at this "kid" Nathan and he comes across so unassuming and you look at his videos and he's so calm in his manner of speech which can put you to sleep, but don't get fooled by his very easy and calm demeanor; I reckon that he's really a super assassin when changes characters by stepping into a phone booth (metaphorically speaking, there are no more phone booths... Poor Clark Kent!).
But jest aside, I absolutely luv and adore that OGFK and can't stop going on and on and on about it. Yeah I know the UFK and the FK2 improved on the handle scales and did away with the mini pry bar but to this date, anyone who sees the OGFK in my hands, gushes about how darn sexy and gorgeous the knife looks and asks about the maker, price, availability, etc. After I saw Eric's post with the OGFK and then your post, it made me think a very plausible scenario, what if I went bare arse broke (not a very pretty sight) and had to choose one CPK... Hmm! Man, I'd be crying my eyes out to having to let go of the Shiv, BD, K18, HDFK, yada, yada... But I reckon that all that I will ever need in case of totally-broke-ass-case-living-under-the-bridge sorta situation, I will take the OGFK, a hatchet and a small Silky saw. If I get released into a forest, I will probably steal a cheap machete from another hobo and hide it down my pants!