Can the date of cocaine use be determined by the level of ng/ml?

someone has a lvl of 2,468ng/ml as of Dec 22, is it possible to determine when they used cocaine? Also is it possible that it was used in August for the last time? My brother in law swears that he hasn’t used since august. i found an empty bag in my bathroom on the 20th. the drug clinic said it’s possible to detect for up to 6 months. Can this high level be 4 months old?