Bosses wouldn't count as secret characters, either, unless you could play as them, which you never could (I'm talking specifically about the original arcade games here; home versions and MKT don't count).
Oh, I am pretty damn sure you could play as Motaro in MK3, I could've sworn. As for Kintaro, I thought you could be him because I seen a couple of character select screen picture's from MK2 and seen Kintaro on a few on them that contained all the secret characters.
You forgot about Noob in MK3, too.
Oh my bad, I didn't even know you could be Noob Saibot on MK3. Hmm, I guess I will have to look into this soon, that is pretty awesome that you could be him.
