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.
Season 1 is a bad example since that was never properly released individually in R2 - there was a 'best of season 1' set with Children of the Gods and the last 3 episodes, while 2 more episodes (IIRC Thor's Hammer and Hathor) were added as a bonus to the last disc in Season 2 - the rest of the season was never released outside of the boxsets
To be fair though, from what I remember the whole concept of complete season box sets never really caught on in the UK for several years - for years we were plagued with best of and single-disc releases - what boxsets did come out were extremely expensive at the time...