My understanding is the AFL have ‘clean’ versions (e.g. no network watermarks) of every match from the 2002 broadcast deal onwards in their archives, but anything before that has the 7 logo as far back as 1996. A quick look at AFL Classics on Kayo seems to back this up.
As to why networks would show a ‘dirty’ feed instead? Probably some Australian equivalent of ‘fair use’ that people have figured out. I remember when the Footy Show wouldn’t dare to show any AFL/Ch7 footage, now they run analysis on Fox Footy clips every Sunday like it’s nothing.
7 must have some clean versions of games from that era. The 1997 Grand Final was shown here in Adelaide during the Grand Final marathon last year. Lost the scorebug along with the watermark and added hideous grey bars at some stage.
A good concept would be to have the current Seven logo and drop the 7plus,com,au and have the positioning of the watermark the same used 2016-19. Here are 2 examples I made that are virtually the same (excuse the grey bars on the top and bottom:
