Thanks for the info, I needed official confirmation.

It seems my guess was about right, so I won't have to change my old emustatus description of the game:

"It seems that, unlike After Burner II, this is some kind of rare title. Probably only released in Japan, After Burner looks more like an experimental game, than a prequel to After Burner II, it has no throttle control, no digitized speech, the ROM is half the size of it's "sequel", and features less graphics and different levels. Boths games have a 1987 copyright year.

Maybe After Burner was an unfinished version of After Burner II, released only to meet some deadline, unfortunatelly not much is known about the japanese classics, so I can only speculate."