Don't know why they numbered them, it's not as if there was any continuity between them
Same reason Playmates' action figures got numbers on them (and you were encouraged to get the "lowest number"). Putting numbers on things is simply a marketing ploy, a way of encouraging people to keep looking and keep collecting. When you put the novels onto your shelf, you can quickly see whether or not you're "missing" part of your collection. (It didn't help the collectors from December 1979, of course, because their early spines didn't have numbers, but anyone who started a bit late - with #16 - knew what books, or what numbers on reprints, to go hunting for.)
Without numbers, some collectors might have been more tempted to cherrypick only TOS novels set during the movie era, not earlier 5YM stories. Again, the cover art can be deliberately deceiving, esp. on those early Pockets. (I recall a fan who refused to read "The Entropy Effect" when they learned it happened before TMP, because they knew all the regulars would survive. Numbering novels can assist in tempting those people to "buy the set anyway".)
When the first "giant" MMPB, "Enterprise: The First Adventure", came along, it was a huge event. It was a special unnumbered book, but no one dreamt there'd soon be two more. Similarly, when "Spock's World", the first hardcover, was announced, it was exciting news: ST fiction had "made it". A science fiction
hardcover novel, on the shelves with all the other first-release hardcover novels in my local SF bookshop. It didn't even have "Star Trek" on the spine! (There was also no promise that "Spock's World" would ever be a MMPB edition. We had to buy it now, and savour the luxury of hardcover.)
Again, the marketing people weren't thinking about what would happen, many years later, when it seemed like there were almost as many unnumbered ST books as numbered books. One main idea of marketing is to get people to buy
in the first place.
Eventually, the high numbering (up to the 90s with TOS) was the reason some people claimed they'd stopped collecting, or the numbering stopped newcomers from even starting. So the numbers were dropped.
I'm kind of pissed off that so many of the really good ones are out of print.
I'm pretty sure that's why ST IV and subsequent movie novelizations were suddenly kept apart from the numbering. I recall reading (in "Locus"?) that ST:TMP has set some kind of record for a movie novelization being kept in continuous print long after the parent film had disappeared from cinemas. For a long time, the inside-book lists appeared to promise that everything numbered would still be available, even on the mail order coupons inside each book!
When those ads were dropped, that's probably when the earliest Pocket titles were finally allowed to start going out of print. (Although the best-sellers often returned. (Several "duology" reprints were rather forced - eg. the "Worlds Apart" duology, which were linked only because both had Klingons written by John M Ford.)
I mean, "The Lost Years?" That book was a big deal when it came out.
I'm sure, one day, we'll get an omnibus of the four "Lost Year Saga" instalments.
Even the crappy ones drew you in with that awesome artwork.
Sure, but I'd say that still works. There are avid collectors out there who always buy more than they can read in a lifetime - I certainly feel that way sometimes; up until "Mission Gamma", at least, I was totally "caught up" with my reading.
Tastes about what makes "awesome" cover artwork continues to change as decades roll by. Those 80s novels, with their Boris art covers and gold-embossed titles, have a style that says "1980s" and, if they appeared on shelves today exactly as they did then, they wouldn't necessarily work in the same way for the potential buyers in the demographics who are ready to buy a ST book they haven't read yet.
