Has it always been possible to select seats on LH segments on UA tix through the United app/website?

I seem to remember on previous reservations there was no option to do so with a message that it was a partner airline segment. However on making a change to a Dec reservation yesterday as a result of LH schedule update I was able to select seats in J for MUC-IAD segment on the UA site.

Oddly, using the LH PNR that same segment shows on LH website as seat selection being unavailable, but once I had selected the seats on UA it updated to show the seat selections I had made. On another LH segment in the same reservation I could select seats on both UA and LH sites.