Checking bags with an overnight stay

[Hokulea]

All,

With the semi-merge of American Airlines and BA I was put in a couple of situations I've not experienced before. A couple of months ago I booked a flight with AA from the US to LHR and the return trip involved a BA flight from LHR to LAX and then onto HNL the next day. The BA agent checked my bag all the way to HNL without me realising it. I picked up the bag at LAX as normal, took it to the hotel and without thinking removed the baggage label.

The next day I realised what I'd done while checking in for the LAX-HNL flight, and after some negotiation got AA to rebook my bag without a fee - using the airport check-in machines didn't give too many options.

So, two questions I hope someone might be able to answer since I'm doing this trip again soon.

Is it OK to leave the baggage label on my bag overnight and just check it in the next day without telling the online system I have a bag to check in? It already knows I have a bag but doesn't know I took it out of the system for an overnight stay. I'm hoping it's OK just to hand it into the usual place in LAX with the label BA put on it.

The other question is has anyone done a trip with the new agreement between BA and AA? I'm trying to pick a seat but there seems to be no way of doing this on either the AA or BA webpage until 24 hours before the flight. I can pick seats on AA flights (since I booked with them) but can't do the same on BA codeshare flights.

And just in case anyone suggests this, I have called BA and the agent seemed as surprised as me that I couldn't manage my booking. Just wondering if anyone has a tip or two. Thanks!