[derefr]

Watch the older videos, not the newer ones.

AFIACT, the videos are a kind of progress log for demonstrating the cat's learning in different concepts. The older videos focused on [demonstration of] learning of more "core" concepts ("food", "water", "pets", "outside", etc.); but since these concepts are now fully "taught", the owner seems to feel no more need to film the cat communicating these simpler core messages, except when they form an interesting sequence or larger idea.

Instead, the newer videos focus on learning of more fringe concepts — ideas that "come up" less often — and so progress is slower in these.

(Note that, watching the videos chronologically, the number of buttons the cat has available grows quite a bit over time. I think the owner thinks that the cat now understands the general concept of associating things-to-be-communicated with presses of word-buttons, and so feels that they can now feed them new concepts faster.)