I haveexperienced no problem having bags ticketed through to connecting flights even when using separate tickets and PNRs where interlining existed. Though in the most recent case (BRU-LHR-YYC-YEG) it was with BA from BRU-LHR and CP from LHR-YYC-YEG when CP was still a oneworld partner.

But I am confused, or just dense. I read the post as being for a mileage run on which you would start off at DTW and go to LGW (ticket 1), then get back on a flight at LGW and go to LAX (ticket 2). And you have just 1.5 hours between arriving and departing. I know FFers do this all the time with mileage runs, and turnaround usually on the same plane they just deplaned from.

But this is at the height of the Christmas season -- from another post you made -- with DTW's notorious snow potential, not to mention the UK's general airlane congestion. All I can say is, may the Gods be with you! And if you miss your connection, that AA will be able to resked you at this heavily booked time of year. (And not penalize you for using back-to-back tickets.)

Also, knowing the general security issues in the UK, and people's experiences at LHR, I am almost certain to reboard a trans-Atlantic flight, you will be required to clear immigration and customs, before checking in for your return flight to LAX. On such an itinerary, I doubt AA would check your bags through in this fashion, and you would have to retrieve them by going through customs, then check them back in airside.

Perhaps I am being ultra cautious, or totally misreading your post, but...