Did Arthur switch dimensions in SLATFATF or was the Earth replaced?

Question

My understanding was that the Earth that Arthur found and on which he met Fenchurch in So Long and Thanks for all the Fish was an Earth that was found in another dimension which the dolphins then used to replace the destroyed Earth.

And then the fling of hope, the finding of a shadow Earth in the implications of enfolded time, submerged dimensions, the pull of parallels, the deep pull, the spin of will, the hurl and split of it, the fight. A new Earth pulled into replacement, the dolphins gone.

This is in contrast with Mostly Harmless, where it is quite clear that Arthur was traveling through dimensions and ended up on an Earth in another dimension.

Yet this seems to be contradicted in the introduction of And Another Thing (which, by the mention of Fenchurch, is clearly referring to So Long and Thanks for all the Fish):

Arthur Dent eventually returned to the hole in space where the Earth used to be and discovered that the hole had been filled by an Earth-sized planet that looked and behaved remarkably like Earth. In fact this planet was an Earth, just not Arthur’s. Not this Arthur’s, at any rate. Because his home planet was at the centre of a Plural zone, the Arthur we are concerned with had found himself shuffled along the dimensional axis to an Earth that had never been destroyed by Vogons. This rather made our Arthur’s day, and his usually pessimistic mood was further improved when he encountered Fenchurch, his soulmate. Luckily this idyllic period was not cut short by bumping into any alternate Universe Arthurs who may have been wandering around, possibly in Los Angeles working for the BBC.

So did Eoin Colfer mess up? Or am I missing something?

Answer 1

The reason for this is a meta reason: you have to look at this from the history of the series itself. The Ultimate Hitchiker's Guide collection includes the following in an Introduction from Adams:

The history of The Hitchhiker's Guide to the Galaxy is now so complicated that every time I tell it I contradict myself, and whenever I do get it right I'm misquoted. So the publication of this omnibus edition seemed like a good opportunity to set the record straight--or at least firmly crooked. Anything that is put down wrong here is, as far as I'm concerned, wrong for good.

He then (humorously) starts detailing how it is that the HGG came into existence. He starts providing a history of its various (re)tellings.

This is where things start getting complicated, and this is what I was asked, in writing this Introduction, to explain. The Guide has appeared in so many forms—books, radio, a television series, records and soon to be a major motion picture—each time with a different story line that even its most acute followers have become baffled at times.

Of So Long... he specifically says (emphasis mine):

At this point I went to America to write a film screenplay which was completely inconsistent with most of what has gone on so far, and since that film was then delayed in the making (a rumor currently has it that filming will start shortly before the Last Trump), I wrote a fourth and last book in the trilogy, So Long, and Thanks for All the Fish. This was published in Britain and the USA in the fall of 1984 and it effectively contradicted everything to date, up to and including itself.

So the takeaway is that things are not expected to be consistent. And it is a de facto franchise tradition that every retelling of and addition to the story must be different and inconsistent with previous ones in some fashion.

Frankly, the only way Eoin Colfer could have messed things up was if he didn't flatly contradict anything.

Answer 2

The replacement Earth in SLATFATF is the 'Earth Mark II' that was under construction in Magrathea in RATEOTU. The pan-dimensional beings (aka 'mice') abandoned it after failing to get the Question to the Ultimate Answer from Arthur's brain (remember: they settled on 'How many roads must a man walk down? 42!"). Then the dolphins bought it and slipped it into place after the first Earth was destroyed, as per their 'Campaign to Save the Humans'.

The bit about the 'deep pull' etc. was just the description of the transportation of Earth Mark II from the Magrathea factory floor to Sol orbit.

Answer 3

And Another Thing takes pages (so to speak) from the later radio series. In them, the idea of the Plural Zone was presented and fleshed out from what Adams fleetingly mentioned in the books.

In them, The Vogons are stubbornly trying to destroy ALL Earths in all dimensions, as they keep annoyingly popping up, making it look like they never got their original destruction job finished.

There's always been some discrepancy between the narratives of the radio series and the books - The Lintillas never made it to the books, but returned in the later radio series.

The new radio series is based on And Another Thing, and will probably try to tie it all together some more.