Does it count as a "word" if only I can understand it?

My son has his 15 month appointment next week and at his 12 month his doctor said he should know at least 5 words by then. He says Momma and Dadda clearly but the other words are hard to understand for anyone who isn't around him a lot. (Fish is Ish, Kitty is Key). Do they still count as words even though he can't fully pronounce them?