I've worked with some old timers and they claim that in the early eighties (circa 83)that 12" square was clean, the eight and ten inch stuff was not, I've read that '85 on was clean immaterial of size. The caveat here is that alot of the glues had asbestos too, regardless of tile size so unless it was brand new glue, I wouldn't take chances without an abatement contractor. They all recomended that unless the flooring was extremely damaged, to place Luan Mahogany down and put a new floor covering over that. The other option would then be floating a laminate floor over the existing covering. I've used embossing leveler over existing flooring and layed a perimeter sheet down over that and extremely good luck.