Why does the Diamond and Pearl sound library only have "Trainers' Eyes Meet"-s for only some of the trainer types in the game?
From Disc 1, I see Ace Trainer, Cyclist, Hiker, Lass, Twins, and Youngster. Disc 2 has Aroma Lady, Artist, Black Belt, Collector, PI, Sailor.
So what about the other types, such as Rich Boys, Officers and Tubers? What music plays when their eyes are met?
The themes are shared amongst groups of trainer classes. It appears the sound library is only listing one type of trainer class that each theme goes with, but other types also share each theme. The groups that share themes are:
Twins, Poké Kid, Tuber & Ninja Boy
Youngster, Camper, Bug Catcher & Pokémon Breeder
Scientist & Collector
Gentleman, Socialite, Rich Boy, Lady & PI
Cyclist, Jogger, Skier & Swimmer♂
Aroma/Parasol Lady, Pokémon Breeder♀, Beauty & Swimmer♀
Worker & Artist
Fisherman & Sailor
Ace Trainer & Veteran
Lass & Picnicker
Hiker, Cowgirl, Rancher, Belle & Pa
Battle Girl, Black Belt, Psychic, Roughneck & Guitarist
Which should make up the full 12 themes in the library. I've bolded the trainer class the library track is named after. Unfortunately, this doesn't seem to be an exhaustive list; for example, the Policeman class shares its theme with the Black Belt group but isn't listed here. The full list of classes from Diamond and Pearl should be:
Ace Trainer • Aroma Lady • Artist • Battle Girl • Beauty • Bird Keeper • Black Belt • Bug Catcher • Cameraman • Camper • Champion Clown • Collector • Commander • Cowgirl • Cyclist • Double Team • Dragon Tamer • Elite Four • Fisherman • Gentleman • Guitarist Leader • Hiker • Idol • Interviewers • Jogger • Lady • Lass • Socialite • Ninja Boy • Parasol Lady • Picnicker • PI • PokéFan Poké Kid • Pokémon Breeder • Pokémon Ranger • Pokémon Trainer • Policeman • Psychic • Rancher • Belle & Pa Reporter • Rich Boy • Roughneck • Ruin Maniac • Sailor • School Kid • Scientist • Skier • Swimmer • Galactic Boss Galactic Grunt • Tower Tycoon • Tuber • Twins • Veteran • Waiter • Waitress • Worker • Young Couple • Youngster
A few of these have their own themes (the gym leaders, team Galactic and so on) but otherwise should slot into one of the twelve groups listed above.
Recycling,
To save time/cost to create unique sounds & effects for everything games often re-use the same sound from somewhere else.
There is probably either a default "Trainers' Eyes Meet" sound for all that have no unique one themselves, or they just share the same sound set as a other trainer.
it's not uncommon for games for example create something for a single object (and name it after it) and then, while the production of the game goes on, use it for something else.
For Example, they first created the Ace Trainers and named everything after them, but once they created the Rich Boys they just added the Ace Trainer backgrounds tuff like the sound to make it more cost efficient because most people wouldn't notice anyway.
