I know. When I used the term it was actually in the sense that the toe cap is the term I know for what's up front and I was having to guess at the term for the heel counter. However, I am perfectly willing to let a shoe maker me when it comes to terminology.
Well good! Actually I'm not overly concerned about terminology as long as I know what you're talking about. I'm sure no one else is either. It just makes it easier to communicate.
That said, saying "heel counter" is like saying "nose nostril." It's redundant.
The correct term is "counter", no more no less--the counter will always be at the heel, just as the nostril will always be on a nose.
For those who don't have access, "The piece of of leather, usually stiffened, forming the back of the shoe, running from the heel upwards. According to OED the term derives from counterfort, a projecting piece of masonry to support or strengthen a wall." (Dictionary of Leather-Working Tools c. 1700-1950, R.A. Salaman, George Allen & Unwin Ltd, 1986)