I hope I didn't miss this question in this thread, I looked.
I have the E+ international subscription. I'm planning a trip BDL-MUC and it turns out I am going to be on LH for the TA flights. So, I plan to buy my tickets through LH so I can buy their Premium Economy.
For the domestic connections, I will be on UA metal. Can I take advantage of my E+ subscription for the flights on UA metal when my ticket is purchased from LH?