The flooring professional that I am speaking with is insisting that because my pine floors are very old (100 years) and have settled for the most part that I do not have to worry about running new hardwood perpendicular to the old floor. This is contrary to what I reading online. It seems that plywood sheets should be put down prior to nailing the new floors down. Is there an argument to be made for the age of the subfloor and directionality?
If I understand your post you want to put a new hardwood floor on top of an old pine floor on a subfloor, right? It's 100 years old and you have no squeeks? I would remove the pine floor, it might be worth some money on the recycled market. Then inspect and repair the subfloor so that it is solid and quiet and then install the new floor perpendicular to the joists over red rosin paper. Check the instuctions on the new floor and be sure that it is acclimated properly. Some installers just leave the floor in your house for 3 days and put it in without checking the moisture content.
I am new to this forum but not new to the game.. You stated in your post 100 + year old pine flooring. GOOD GOD MAN REFINISH IT!!!!! They don't make flooring like that anymore. Or hey here is an idea, I will come remove it for you free of charge and you can start fresh. But I keep all the wood.