Other mistake: When Cat picks up the can of Leopard lager which is invisible to Lister, he shakes it, pops the cap and sprays Lister with foam. The foam is visible but the can remains invisible, and that makes no sense. If we are seeing the scene from Cat's point of view the can and foam should both be visible, and if it is from Lister's then neither should be.
Plot hole: At The End, Kryten, Rimmer and Lister are in a lift facing off six gelf shapeshifters - two copies of each real person, in a Mexican standoff. Nobody knows who to shoot, as they might shoot the real person instead of the shapeshifter. But the real people know they're real - all Lister has to do is shoot the two fake Listers, Rimmer shoots the fake Rimmers and Kryten shoots the two fake Krytens, problem solved. Not to mention Lister is now a soulless, unfeeling killing machine. Earlier he shot and killed a shapeshifter who could well have been Cat - he didn't know it was a shapeshifter and by his own admission he didn't care. We have already seen how fast on the draw he is - why didn't he just open fire on the six shapeshifters, Kryten and Rimmer in order to ensure his own survival?
Suggested correction: The point of a Mexican standoff is no one is in a position to shoot first for fear of being shot themselves. We're told the shapeshifters have no problem killing each other, so as soon as the real person starts to shoot, everyone may start firing, which could result in a real person being killed. Additionally, the only time all 9 are pointing guns at each other is in the lift. Before that, it's 3 groups of Listers, Krytens, and Rimmers, so no one is facing off with their shapeshifters. The only safe way to shoot the 6 shapeshifters would be to do it at the same time, and there's no way Lister, Kryten, and Rimmer could coordinate that. And, like all Mexican standoffs, it can only be resolved from outside help.
Character mistake: Upon hearing that Lister, Kryten, Cat and Rimmer have travelled from Albion - England - to India the woman in the market expresses surprise that they have travelled "halfway across the known world" just to buy lemons. In 23AD travelling from England to India was all the way across the known world. The Americas, Australasia and China were completely unknown at the time.
Character mistake: Surely, a know-all like Kryten would know that although lemons are not native to the Middle East, Babylonian traders imported lemons into what was then Judea some five hundred years before Christ was born, and by 4BC, they were quite common in the area, albeit as a pricey imported delicacy. The Dwarfers wasted half of their epic overland trek.
Continuity mistake: Rodon is revealed to be the Cat's older brother, and the rebelling cats refer to the Red Dwarf itself as the ship of their birth, but in Psirens, it was revealed that the crew spent 200 years in deep sleep while tracking Red Dwarf. This appears to have been forgotten.
Revealing mistake: After the crew transport themselves out of the book depository to escape the FBI, the astronaut helmet is transported afterwards and the two FBI agents start shooting at the box the helmet was placed on. When the box is shot, there are no bullet holes left on it.
Timeslides - S3-E5
Factual error: The newspaper detailing the bomb attack on Hitler lists the date as "Tuesday May 4 1938." May 4th, 1938 was a Wednesday. (00:09:15)
Revealing mistake: When the Polymorph, posing at the snake, jumps on Lister, it is apparent that the snake on Lister has been replaced by a plastic inflatable replica that has no features and does not move. (00:10:05)
Continuity mistake: When the Cat is eating the food set out by Lister, there is a cloth on the table. When Lister is asking where the other kitties are, the cloth is shown near the centre of the table. Rimmer then says he wants it off the ship, and the cloth is suddenly further to the right of the table. (00:27:45)
Continuity mistake: When Lister is revising for the exam, he opens a can of beer which sprays foam onto the table, and onto his cigarettes, when he opens it. A few seconds later, the sprayed foam disappears from the table. (00:19:30)
Continuity mistake: When Rimmer is talking to Lister before the exam and says they are friends, Lister replies "When?" Lister has a can of beer on the bunk, with the label facing the camera. Two shots after, the label is suddenly facing away from the camera. A couple of shots after that, the label is suddenly facing the camera again. (00:23:15)
Confidence and Paranoia - S1-E5
Continuity mistake: When Confidence is telling Lister that his song was the greatest love song ever, Lister has his right hand on his lap, but in the next shot, his right hand is suddenly on the guitar strings. (00:19:35)
Continuity mistake: When Lister is questioning how they can remake Casablanca, he is holding the video tape, but in the next shot, the tape has disappeared from his hand and is touching the control panel. (00:04:40)
Continuity mistake: When Lister is getting ready, he pulls his trousers off the table, causing the boot on the table to wobble. In the next shot, the boot is entirely still. (00:10:35)
Revealing mistake: When the Outland Revenue guy breaks Rimmer's thumb with the mallet, the mallet does not touch his thumb, but instead his fingers. (00:28:35)
Continuity mistake: When Rimmer falls asleep whilst Lister is doing the jigsaw, there is a whisky bottle on the table. Later in the episode, when being viewed on the black box, the whiskey bottle is no longer on the table. Lister could not have thrown it away since he left the table to the Hologram Simulation Suite at The End of the scene. (00:10:20 - 00:19:35)
Continuity mistake: When Lister is doing the jigsaw and Rimmer starts singing in bed, the pint mug on the table has nothing in it. Later on, when Lister returns after giving Rimmer his memory, an inch of whisky has suddenly appeared in the bottom of the mug. (00:10:20 - 00:19:35)
Suggested correction: Lister can only see M-Corp products and M-Corp employees. Cat is not an employee of JMC or M-Corp, so he disappears. Lister is the only member of the crew who is employed by M-Corp at this point.
Suggested correction: Cat was a descendant of the cat Lister brought aboard Red Dwarf. Would it be possible that the new owners might have stricter security controls, and Lister was sent to Stasis for a different reason?
Andy Benham ★
Inventing Deux ex machina explanations for a plot hole doesn't make it any less of a plot hole. M-Corp erases all of the Jupiter Mining Corporation's equipment, personnel and infrastructure from Lister's life. In no way is Cat a part of that. He has no connection at all to the Jupiter Mining Corporation, and until he meets him in Episode 1 no connection to Lister, either.
If M-Corp only erased JMC equipment from Lister's life, then Kryten, who belongs to DivaDroid and not the JMC, wouldn't have disappeared either. He disappears as he doesn't belong to M-Corp, not because he belongs to the JMC. Cat has no connection to M-Corp, as he wasn't a part of the JMC (as you pointed out), and is therefore erased for Lister.