So suppose you have these photos that a photographer sent you a year ago to play with if you want, or not, and you decide you feel like retouching for fun to try some new things. You end up LOVING it, and decide to do a whole editorial with the photos. You even name it and add the credit of everyone including you, the retoucher. This is not going anywhere but in peoples portfolios, no magazine, not paid. The photographer asks you to remove the credit for the retoucher because an agenct at a MODEL agency told him not to credit his retouchers.

Thoughts?

Why would a retoucher not get credit?  It requires talent the same way photographers, MUA, hairstylists, and models have talent.  If you're contributing, you should get credit in my humble opinion.

Having said this, I never use retouchers unless it's a one off job and I can bill the client.

He should then use his own versions.
Another reason can be that he does not want the agency to know that he needed someone also to get the result, or maybe the agency actually wants clean images with no text.

Ditto!

I ran into a problem as a photo editor where we had to heavily retouch an image, but I knew the photographer would be sensitive about how we credited the work. He wants everyone to believe his celebrity subjects are so perfect, it's just a matter of him "pointing and shooting" the camera at them. I chose the term "post-production" to add the retoucher's name to the credited crew, and everyone seemed very happy with that solution.

Let me put it this way.. this model wasn't apart of that agency, these images aren't being submitted to anywhere. The model doesnt even model anymore. lol

How I handled the situation:

Gave him the uncredited version, and told him that it was the last free retouching I did for him. He was extremely nice after that.. go figure.