This has been a confusing issue for a while now. I was under the impression that a J passenger without any other status [i.e. STARGold, MLL Club, etc.] could only use the MLLs, vyr at just the ones in YVR and YYZ. This appears to have been extended across the MLL system, but not to affiliated clubs.

So the LH "guardian" was correct in not permitting you access the other day. US airlines do not permit lounge entry on NAmerican F or J flights, so in this regard AC is consistent with the competition. Sorry.