Generally the continuity in 2001: a Space Odyssey is pretty good. But one exception is probably the four iterations of the front panel on the EVA pod spacecraft.
A: the front panel as it appears on the three full-sized pods in the pod bay. All have machined metal (probably aluminium) cylindrical front cameras, not the black Nikkor camera lens used to depict HAL 9000. Details are simple, and none of the rings have coloured curved lines applied.
B: The front panel as it appeared in most of the space scenes. Basically the pod bay pod, but the metal camera lens was replaced with the black HAL lens.
C: The front panel as it appeared during the attack scene and one or two of the space scenes. Essentially it’s the previous version with the addition of curved black and red lines on the rings.
D: Finally we have the superdetailed panel that was built specifically for the closeup shots that flash on-screen during the jump cut sequence. It appears to have the same basic underlying model infrastructure, but all the detail parts have been replaced.
Numerous additional greebly details have been added on. The lattice object on the port side (right side of picture) has been flipped upside down, cut back on the side, and encrusted with numerous extra details. The curved colour line decals are similar to the full sized pod version, but have numerous differences in detail and geometry.
I don’t know with certainty why these differences exist. I only documented all this nonsense because I am building a replica model of the EVA pod and had to make some decisions about which panel to make.
The usual and perfectly reasonable theory, though it’s complete conjecture, is that Kubrick decided during the course of filming to show that the pod front camera was controlled by HAL so that the audience would know that the pod was remote controlled by the computer at that point. But the pod bay scenes had already been filmed, and Kubrick had no desire to re-film them just to have a revised front camera lens.
As for the differences of the closeup superdetailed panel, the usual conjecture here is that Kubrick decided that the standard pod panel didn’t look very good in extreme closeup and asked the art department to make a new version. And neither he nor the art team were particularly bothered by the continuity error that resulted.
Indeed, in normal cinema viewings these differences are difficult to make out. It’s only by relentlessly examining static images that you can figure most of this out.
The narrow strip above the front panel, which has a series of vents cut into it, has a couple of detail differences (not shown here). The main difference between the full-sized pods is a grey rectangular block, inscribed with lines, which is present on one version of the pod. The superdetailed panel has numerous additional greeblies in this strip, though only the lower half is visible, and has some structural differences to the edges of the recess.
There are some very minor differences in arm design between the static pod bay pods and the pod which had articulable arms. These alterations were clearly designed to accommodate the moving parts.
The rear of the pod on the port side has a red detail box. This was designed to be some kind of removable energy module, and is seen missing in at least one pod bay shot. (The text next to it reads REACTANT CELL)
The two cylinders to either side of the step had two vents cut into them. These vents were horizontal in the pod bay scenes but vertical in the space scenes. It’s not known what these cylinders were meant to be. They couldn’t have been engines or exhaust pipes. There were two words printed next to each one, but the first word is not legible in any known photo. The second word is legible in one photo, and that word was COUPLING.
The majority, though not all, of the plastic model kit greeblies have been identified. The full-sized pods (ie: not the superdetailed panel) had the following kits:
Airfix SR-N1 Hovercraft 1/72 287
Airfix OO Travelling Crane 205
Airfix OO Locomotive Turntable
Airfix B-29 Superfortress 1/72 781
Renwal 1/200 Polaris submarine (I don’t know if it was the “George Washington” 651, the “Ethan Allen” 652, or the “Andrew Jackson” 654, or whether they’re all identical in terms of the parts used in 2001)
Most of these kits have been re-released by Airfix or Dapol, but the Renwal sub remains scarce and extremely expensive.