In the first episode of series 6, Psirens, Lister admits essentially losing Red Dwarf due to not being able to remember which planetoid he has parked it on. As a result, the 4 of them are confined to the by far smaller scouting vessel Starbug. The real life truth is that much or all of the Red Dwarf set was lost inbetween the making of series 5 and 6.
Cat is supposedly descended from Lister's cat 3 million years earlier. There wouldn't be enough genetic diversity in such a scenario, and the increasing levels of inbreeding would have wiped the cats out long before evolving into humanoid form.
In the intro sequence of Series 1 and 2, a man in a spacesuit (Lister) is seen painting the exterior of Red Dwarf and the camera pulls back to reveal the Red Dwarf spaceship and we see Red Dwarf flying towards the black void of space and Series 3 - onwards, a montage of the episodes from each season is seen during the intro sequence.
On the extended version of Series 7, in episode 1, instead of the last scene being Lister getting beaten up by the rest of the crew, he finds out what really happened to the curry. Instead of it being destroyed in the flood, Lister uses the time machine to go back and save it before the flood occurs. The episode then ends with Rimmer tricking Lister into flipping the switch which detaches the back end of Starbug, leaving Lister alone in deep space with the curry.