Theo: Below 80-85 or so, there seems to be an undocumented feature that makes the armor type to be one you are more likely to gain skill on. For example, most of my BODs when I was in the 70s were the leather parts I could do, thigh boots, cloaks and robes, with the other parts occurring, but not as often as true randomness would suggest.
So, while 70.1 is sufficient to have a chance at all BOD types, there's still something playing with the numbers on the "specific item type" that makes things dicey for the first 10-15 points, maybe as far as GM. My 75 tailor skill craftmule (has tailor only for BODs and add-ons) pulls a LOT of robes, leather sleeves, leather gloves, and leather gorgets (1 in 3 exceptional, and standard chances for special leathers - but STILL stuff he can make between 50%<100% skill, much more than 100% success or no chance to make)