If i remember correctly there was supposed to be an Army of mando supersoldiers at one point in during the pre production phase on empire strikes back, and then because it was deemed too expensive they made the general design into Just boba fett and made him a bounty hunter.

It was not mentioned at this point that they were clones but it would not surprise me if that was an old idea of lucas re-used in the prequels.

I think though i might be wrong that the mando supersoldier was just supposed to be the new stormtrooper in episode V.

It makes sense for the rebels to have lots of goons, imperial henchmen, etc. for cannon fodder for the rebels,lol.