Yeah, well, not all the horses were covered. Mostly just the mounts of knights showing off their coat of arms. That's about what we have. However, even the best-known researchers about this period pretty much all said that horse armor was transitional in this time - some was appearing, in limited quantity, but exactly how much is quite a mystery. The decorative cloth used to protect the horses from the desert sun was sometimes reinforced with quilted cloth, leather, or various bits of metal, but exactly how much was anybody's guess. (One dig from the period found one section of maille for a horse - at least they thought it was for a horse, from what was left of it - but the same dig also found a mule that, from the stuff around it, appeared to have been used as a combat mount as well... you win some, you lose some. That was a pretty recent find.)
And I don't trust carbon dating as far as I can throw it. Not since that UCLA lab tested a live sealion and it said the thing had been dead for 6000 years. (Due to diet and effects of salt water, sea mammals have a MUCH lower C14 level than the human fingernail clippings they used to calibrate the machine.) Calibrating those things to get a useful number is almost impossible, unless you have one item with a date stamped on it and can confirm that a huge number of factors were completely unchanged between the two years. And since you don't know what the second year is, that's hard to do unless the items come out the same date. Otherwise, even getting close can be tricky. You don't have to be much of a physicist to see what's wrong with the theory... it assumes a bunch of unknowns that, were they known, could have a HUGE impact on the result. Don't trust Carbon-14 dates... if they get you within 500 years, you're lucky. (Sometimes they're incredibly accurate, and that throws you off even more when they give you a result that doesn't figure.)
Raz built, or borrowed, the swords ... I'm not sure exactly which sword you're talking about. The only ones added specifically for this mod were the Muslim blades, all the others were stuff floating around for the M&B community. They weren't sorted all that carefully - if they looked anywhere close to period, we sort of figured one of them might have been there, and threw it in. There are some obviously Norse weapons there too, which would be out-of-date by the period, unless somebody just liked the older style or was using their great-great-grandfather's sword (possible - Japan wasn't the only place to consider swords as family heirlooms)... but what the heck, it's a game not a doctoral thesis. A few corners have been cut, here and there, at least until somebody gets around to doing all new sword models specifically for HW. On that note, we're also waiting for pigs to learn to fly.
Consider that Raz is making at least 90% of this mod himself, and so he's cut a few corners. I try to help, but my only real expertise is in killing things ... of which I know a good deal, but I can only model damage for the blades I can see.
Osprey's books are moderately reliable, at least close enough to base a computer game from. They're not always real specific or entirely clear what they mean, but again, for a game we can likely extrapolate the missing bits and be close enough.
Anyway, yeah, the social questions were tough ones. If it was easy, anybody could handle it.