Salaries only update once per season, so that's why they're inaccurate sometimes.
That's not the problem. When you check 34yo player there is no chance that he poped like 7-8 points over one season - and that's the difference beetwen 100% and 99%-100% cap.
I also doubt that you can make 8 points over the cap, couse when you reach it, training slows down like 3 times (from what people say) and player is also over 29 yo in most cases.
The gap is to big, the toool is not accurate at all.