A -6.5 favorite winning by 7 covers; winning by 6 wins the game but loses the bet. ATS records exist because raw win-loss records say nothing about betting value - a great team laying huge numbers can be a terrible bet. Note that ATS results depend on which number you graded against: a team that “covered -2.5” may not have covered the -3.5 you actually bet.
Grading covers programmatically needs the exact line at bet time - which is what timestamped odds and the 1.7M+ closing lines in ParlayAPI's historical archive provide. Backtesting an ATS angle against real closing numbers (not consensus averages) is the difference between a real result and a mirage.