according to ProFootball Reference they are "official"...but perhaps they are wrong idk
Tkl - tackles. We have tackle data for all players who were active in 1994 or later. Prior to 1994, the tackle data is unofficial, inconsistently recorded from team to team, and incomplete in our database. Also, before 1994, some teams recorded assists while others didn't, so we have lumped tackles plus assists together in the tackles column for those years. From 1994 to 2000, tackles were not an official stat, but were recorded consistently and should be complete in our database. From 2001 to the present, tackles have been an official statistic.
NFL.com does list tackles
it really doesn't matter I don't think weather or not they are "official" or not...whatever