Learning through mistakes...
 

Rebuilding a 1983 944 (my first). Removed the transmission to get to the fuel tank (needed repair). When I separated the drive shaft at the coupler, I failed to mark the coupler on both sides. Of course when the transmission separated, the coupler stayed on the side I marked (transmission side) and pulled off the drive shaft. I haven't turned the drive shaft and can guess at the position because the head of the bolt in the coupler was visible in the cutout in the transmission housing. Is there any way to recover the alignment if you have not marked the shaft?

I don't think it matters

In write ups I've seen, it says to mark them so you can put them back the same way. I don't know why. Maybe so it continues to wear the same way?

When I replaced my transmission, I lost my markings. So I just put it back in. Didn't seem to matter.

Its a coupler. Don't worry, be happy. Worse things can and will occur. Grease it up prior to re-assembly. If you don't have things lined up properly on install, you won't be able to get it back together. You'll see. :)

Doesn't really matter... When I dropped my trans for a clutch replacement it went together fine. No excess vibrations or wobbling at the connection back there. You'll notice that it has been drilled and balanced, so I don't think it matters exactly how it goes back on.