as I said in my intro text - there is no seventh series...
these covers follow how there were released in the UK - so what some episode listing sites list as seasons 4 & 5 (which were both 2 episodes each), were released together as Series 4 in the UK...
so consequently, Series 5 in the UK is listed as Season 6 on the sites, and Series 6 is Season 7.
if you check the episodes list, they only made 22 episodes and they're all included in these covers in the correct showing order.
hope that helps.