No harm, no foul!

Even though you were aware of the proper location of the seal someone else wasn't and has learned how to properly install a bulkhead. Hopefully the thread has saved someone a leak! Leaky tanks suck!
When I made this mistake it was because I wanted to install a bulkhead "backwards" with the flange on the outside of the tank so the tank would not have to be as far away from the wall. Once I figured out why I had a small dripping leak I moved the seal to the flange side of the bulkhead... which was on the outside of the tank... and the leak stopped. 15+ years later that tank is still running fine, with the bulkhead flange on the outside of the tank, the seal on the outside of the tank and no leak! Sorry if I sounded rude... just trying to let others learn from my mistakes.