Heck I use the TDC for over 90% of my attacks, so my perversion seems to be harmless so far.
But who knows, it might yet take over my life and cost me my marriage and fortune. So far, I have it under complete control, however....
Yes, so long as you are shooting zero gyro angle shots, your speed and heading do not matter, and target speed cancels out of the solution equation as well, making a TDC which does not know your own course and speed "just fine."
Thinking out loud about possible exceptions, a nasty situation is when you've shot, the convoy splits up and a wounded target is limping away. You must follow. Much better than the 180º shot (because a course change by the target, plus the narrow aspect of the stern shot means lots of misses) is a shot that extends parallel to the target course and then turns 90º or so to impact at a near right angle to the target.
And it still works well, as if you match the speed of the target, you have an unchanging relative position and the TDC doesn't need to know your own course or speed. Your solution remains valid for quite a few minutes probably. But you can't do that shot without a TDC, no matter whether American or German.
On your second point, you know, you might just be right there. Without the PK, the German TDC really didn't NEED to know the actual courses of the target or submarine. The only limitation would be that you couldn't change course without destroying your TDC solution. In the American boat you can change course and the solution remains valid.
Deep, dark and nasty secret. With the technologically advanced American TDC/PK, although YOU can change course and speed without ruining your shot, the target can ruin the shot by changing course and/or speed because that information must be manually updated by you. Live by technology, die by technology!
I'm going to have to try it and see what happens! The attack map should show clearly what the situation is. If you change course and the gyro angle remains the same the TDC doesn't know what course you're on. If it changes to still hit the target, the TDC does know.
Just guessing here, I'll bet that's a function of the position keeper and not present in the German submarine. Good catch!