Awesome! Thanks a lot for the links.
Yes, I am developing a Cave-inspired shmup, C++/OGL+Lua game logic, the engine is done, but I am curious now on how they did certain stuff, boss anims, stages, etc. it is mostly a curiosity since in Lua we can do anything regarding stage logic and gameplay.
Also I've searched about how they did the pixel art, what (obscure) programs, methods.
My fear and almost certainty is that it was quite hardcore

, enemy animations by hand in the code, and pixel art with the available programs of that time.
Still, nevertheless, source code even in its most primitive form would be awesome to study and learn some tricks from the masters

.