Regarding the discussion on whether this was a Rambo II rip-off or not

There's a lot of discussions on whether this movie ripped off rambo II or not, some saying that it was Cannon who heard about Rambo II and fast tracked the filming of the two MIA movies, and some even saying that Rambo II ripped this movie off.

In the book Hollywood a go-go from 1987 that is about Cannon, according to the writer Andrew Yule, the idea for Missing in Action didn't come from Cannon at all.
It was Chuck Norris who had the script that had been written for him, and he had also been a part of the development and writing, and he called Golan and Globus up and offered them the chance to produce the movie.

At that point Chuck was a well established action star and he had a few hit movies under him, so Golan and Globus jumped at the opportunity with only one demand, that they would shoot two movies back to back to save money.

According to the book the budget for the first Missing in Action was only $1.5M and it became one of Cannon's biggest hits.

The book does not mention Rambo movies, but rather implies that it was loosely if not based on than inspired by Uncommon Valor with Gene Hackman.

The book does not mention which script Chuck originally had, the first one or the sequel (The Beginning, which was originally going to be the first one).
It only says that the idea for filming two movies was a demand of Cannon's.