The cat portraying Frankenstein in the alternate universe is a small kitten, so too young to have been pregnant at the time and to have spawned the ancestors of Felix Sapiens and the Cat.
Even though the Kochanski featured in this episode is from an alternate universe, she has somehow gone from being a happy-go-lucky Scottish character from Glasgow, to a snooty, uptight woman with an accent from England's Home Counties and a different attitude, values, upbringing and nationality.
In the flashback scene on Red Dwarf, as Lister and Rimmer enter the locker room, in front of them is an extra who was also one of the customs officers that they've just walked away from.
The revelation that Lister is his own father creates a rather large problem: In the Series 2 episode "Better Than Life", he recalls his father's funeral when comforting Rimmer after the latter received a letter from his mother informing him that his father had died. Lister was probably adopted, so he would be speaking about his adoptive parents, rather than his real parents. Also, in the Series 5 episode "The Inquisitor", after Lister and Kryten are declared "unworthy of existence" by the episode's title character, an alternate version of Lister, described as "coming from the same barrel" as the other one, somehow takes his place, despite the fact that if the original Lister never existed, there should be nobody by the name of Dave Lister at all.
Lister says he married a GELF because they needed an engine part. However in Emohawk: Polymorph II (1993), it was an oxygen generation unit that they needed.