Poor wording on my part.
The earlier seasons were available in season form prior to season 7/8 releases, however they were some way behind the individual releases. Season 1 for example came out in season form 4 years after the series had aired on TV and at least 3 years after the individual DVD releases.
To be fair, SG1 wasn't the only series where that happened. Farscape was similar.
That carried on until season 5, when they eventually caught up to a point.