“…….. appear to be the Mk II versions. They typically have to be worked on to get them to 100% reliability.”

Balderdash. I’d never even heard this one before. One of the strong points of any P35 was, they always went BANG.

The T and C series guns were forged frame pistols. These were the first external extractor guns and were considered some of the finest, best finished guns produced by FN. (Obviously the “Browning” guns were produced by FN as well)

The mk 2 guns were also forged frame but had slides with a “rib” and milled/non removable front sights. The examples I’d seen all were Parkerized, not Blued.

The mk 3 guns were cast frames that (allegedly) handled the more extreme pressures of the .40 S&W and subgun 9mm which the Brits were supposedly firing in their issued P 35’s.
The older, forged frame guns were not holding up to the the increased pressures of .40 S&W and +P+{?) ammo, hence introduction of cast frames. I’d imagine the cast frame guns were cheaper to produce as well.

There’s a noticeable difference in girth of the forged vs. cast grips, subtle but noticeable. The cast frames are obviously thicker.

I looked on Arms Unlimited web sight HK. I couldn’t even FIND a P35, but I’m old and not tech savvy.
FWIW; I could never leave a P35 I owned alone, with a NINE pound SA trigger being within specs, I always improved my pistols so they were more “shootable”.
As all gun guys know, this always ended up going down the Rabbit Hole…..
I am FAR from an SME on this platform, but I’ve owned and “improved” a number of them.