I too pride myself on owning all Cathe's videos, so I understand your frustration when you learned that there are 'classic' videos floating around that you don't have in your collection.
If it helps, someone is selling this tape (Cardio Step Challenge) on Ebay right now. I don't remember where I got my copy - it was either Ebay or the Dollar store. Anyway, although the outfits and background on this tape do look a little dated, it's still a really good video. Not nearly as intense as Cathe's later tapes, but you can still get a good workout.
I also have "Fit & Firm". It has the same beach-look background set as the Cardio video. Personally, I like "Fit & Firm" A LOT. It's one of my favorites - if I am only evaluating the quality of exercises. It is definitely more toning than muscle building, but since I have no desire to build additional muscle mass, this is perfect for me.
My only complaint about this series is that there is quite a bit of "whoo-hooing!" in the background from some of the ladies in the class. If you can get past that (and the lace biker shorts) then this makes a nice addition to your video collection.
The bottom line is that there is no such thing as a 'bad' Cathe video. She has blessed us (and spoiled us) by consistently making high quality, professional exercise videos that are lots of fun and yield great results.