Okay, this is getting OT and very nerdy, but I don't care.
I had to look it up, because it has been too long since I have read the later books. The Agrajag story wrap up is in the third one, which theoretically makes it part of the original trilogy
. But I agree, a large part of the third book is not up to the standard of the first two, and I think there is a reason for it (see below).I read the fourth and fifth book a long time ago and found them... much less entertaining than the first two. Recently I learned that "someone" has written a book in 2009 that is now counted the sixth book of the trilogy because DA's wife approved it, and here are also four more radio play series that were published after DA's death. Personally, I rarely like posthumous work of authors being finished by other people after their death. It rarely ends up being good.
In my opinion, the original radio plays (two series consisting of six plays each) are the best incarnation of the guide; I have listened to them many, many times with childish joy. After the second one, the books deviate quite a bit from the original story lines, and while the first two books pretty much follow the line of the first radio series (the first six radio plays) truthfully, only bits and bobs from the original radio play make it into the later books, and the second series' story line is pretty much abandoned in the books.
And let's not talk about the movie. It was terrible.
. But you're right.