So that lead me to try killing the steam process to see what would happen.... This put the 8.1 box in the same situation as the 10 system.
Then restarted the steam client on both systems.
All is now well on 8.1 and on 10.

Problem resolved.

Some more information. The system that is having this problem is Windows 10 Pro x64. I just tried installing Panzer corps ( and all dlc) on an 8.1 pro x64 system. That install went fine and all DLC are avaliable to play. I then compared the Panzer corps directories on the 2 computers and they are th...

I purchased the Panzer Corps Collesion on steam. The base game and ALL DLC show in steam that they are installed. When I run the game all I have access too are the standard Panzer Corps Options. When I click on Afrika Corps Icon it tells me I do not own that and wants to know if I want to purchase i...