I am pretty certain that there were a number of seperate gods in those days. Some of these gods were related, some forming triads of particular power, others seen as different aspects of the same god.

But I find it highly doubtful that one god known for goat horns would have been portrayed as having rams horns.

This is the times of the pre-literate - visual communication was therefore of increased importance - images had to convey an obvious message - one re-inforced by the bards. This was also a time of strict adherance to the bards message - the bard being the bringer of truth - written words could lie but a bard could not. I think everyone knew that such and such a god had X horns, and they all know why he/she had them - they would have been part and parcel of the god myth.