How do I use Quicktime Player 7 Pro registration for second computer? View order history only goes back 18 months. When I enter my key in QT7 it just tells me to buy again.

You are legally correct but not precise on the technical issue. After writing my question, I found an archived digital copy of my license and saw that it forbids multiple computer installations. Thus I assumed there was a built in technical block. I downloaded a slightly newer version of Quicktime Player 7 (ver 7.7) and almost purchased a new Pro license. Before deciding to install the newer Player 7 on my current Mac, I deleted the older version (7.6.6) on the same Mac. That's when I discovered that there had somehow been two copies installed. Using the Launcher was making the non-Pro version open. Okay, so the surviving copy was the one that had been upgraded to Pro in May, 2014 when I purchased it because that's what I found out when I opened it yesterday. There is no technical block to prevent its usage. It's still Pro. The license is apparently an honor system, meaning I'm supposed to delete either the copy on this Mac or the copy on my older Mac that I very rarely use. By the way, the newer version of Quicktime Player 7 would not install because I also have Quicktime Player version 10 installed. But the older 7.6.6 Pro that I almost deleted from the newer Mac, works fine. Presumably, you cannot install any version of Quicktime Player 7 anymore if you have Quicktime 10 already installed. But if you already had Player 7 or 7 Pro installed, it still works. Quicktime Player 7 Pro is a fickle installation that may or may not survive future changes in the Mac OS. I hope it keeps working but I think it would be smarter if version 10 had a Pro option.