Out of print / limited run print for some reason e.g. copyright / rightsThis has also happened to other series such as Beastmaster season 3 and the complete series boxset which was withdrawn due to rights but a few boxsets did manage to get out before the recall.
I just completed my set with a $50 ebay purchase for season 3. I figured it was about as low as I'll ever find it. ('Very good' condition; all the new ones were at least in the $70-plus range.)
Interesting note -- on the Forever Knight pilot episode (on the first DVD set), it begins with the 'CrimeTime After Primetime' billboard intro. (That was the CBS umbrella title of latenight shows it was airing under at the time.)
Then, when the actual show starts, the 'CBS - In Stereo' overlay pops up, just like it did when originally broadcast on CBS. It makes me wonder if the episode was taken from an over-the-air recording of the actual broadcast.
I haven't finished viewing the entire set yet, but so far none of the later episodes I've watched have these anomalies.