Yeah, that was in the second radio series. There's a lot of stuff there that never got adapted into any of the other versions.
I think they should remix the elements in a new way rather than just try to exactly copy a previous version. I mean, everything up through Magrathea is pretty much the same in every version, but after that, and particularly after prehistoric Earth, the different incarnations tended to go off in their own directions or put the pieces together in distinct ways. And I like that -- I think it's part of the franchise's character that the different versions are unique rather than just the same thing over and over. I was actually rather disappointed that the radio continuation from a few years back adapted the later books as exactly as it did. I think it would've been more interesting if they'd taken more of a new approach. (I did like the way it retconned the ending of Mostly Harmless to be less depressing and ghastly, though.)
It seems to be common in British multimedia franchises of this sort that each version is different rather than a direct adaptation. Red Dwarf is similar, with the novels telling alternative versions of the episodes' plots and eventually veering off into original material. I think I've heard of at least one other franchise where the books based on the show were pretty different from the show, though I'm not sure what it was -- maybe Blackadder?