I have a business class ticket, issued by AA. The first leg was Bengaluru (India) to LHR on BA, and connecting at LHR to MIA by AA; the connection time was 100 minutes. (I believe MCT is 90 minutes for BA arriving T5 to AA connection at T3 -- don't ask, this was the only choice available).
My BA inbound to LHR was delayed by 30+ minutes, and I was told by BA staff to "run, you can make it" - and so I did, arriving at the AA gate 35 minutes before departure.
But when I tried to board, I was told BA had already re-booked me for LHR-LAX-MIA, arriving the following morning.
BA did not tell this to me, and I found out only when I went to the AA gate.
My assigned seat had been given away already.
I really did not want that, and a very resourceful AA person managed to make some calls, and found me the last business class seat - and I was one of the last one to board (20 minutes before scheduled departure).
All this happened two days ago.

Here are the problems.
(a) I have been given mileage credit for BLR to LHR (it posted yesterday) but not for the LHR to MIA flight (as of now).
This is just to give context, and the least of my problems.

(b) More worryingly, when I log in to my AA account, it still shows the original AA flight from two days ago, LHR to MIA, as yet to be flown.

(c) I also had to make a date change for the return segment (MIA-ATL, ATL-LHR-BLR), so I called in this morning.
After some effort, the agent got it done, but I still do not have a new ticket number - and I cannot find the new ticket number when I login, even though the new dates show.
I will be flying MIA-ATL in a couple of days and then from ATL-LHR-BLR after an overnight in ATL.

(d) When I login to BA website (because the ATL-LHR-BLR, yet to be flown, are on BA), it does show the two segments to be flown on BA along with the MIA-ATL yet to be flown on AA.
(The BA site also shows the BLR-LHR segment already flown - but even there the LHR-MIA is missing). I am able to select seats, etc.

(e) Of concern, even after the change in itinerary, the LHR-MIA still shows up as to be flown on the AA website.
When I assign a seat for MIA-ATL, that same seat number automatically shows for both the LHR-MIA and the MIA-ATL flights.

(f) Was then transferred to AA web support, and they claim no problems.They claim do not see the LHR-MIA flight on their side now.

Suggestions?
Thanks in advance.

To be honest nothing that you're seeing is that out of the ordinary for your situation.

1) If the LHR-MIA doesn't post automatically, then fill out a missing miles request at aa.com.

2) Sometimes on complex, international itineraries like this flights that you have already taken still show up for a day or two when you look at the reservation at aa.com.

3) For the date change on the return segments, it sounds like the ticket just hasn't been issued yet after you made the call/change (again it can be 100% normal to take a bit for a complex itinerary involving partners).

4) I would just give AA a call back (to the regular reservations number, not web support), tell them you recently made a change to itinerary XYZ, the flights are in a few days but you haven't received the new ticketing email yet, ask the agent to verify that everything looks OK and if they can push it through any quicker.

Give it some time and follow up as JJeffrey has recommended. you will get your credit

First, thanks to JJeffrey for the quick response, much appreciated.
Update:
1. The miles for LHR-MIA posted now.

2. The LHR-MIA segment does not show up now when I login to AA website as a pending flight.

3. But I still do not have a new ticket receipt email, after the date changes yesterday for the MIA-ATL and ATL-LHR-BLR segments yet to be flown.
The AA website does not have an option to print the e-ticket receipt.
Called AA, and an agent gave me the newly issued ticket number.
But when I tried to check that at
https://www.aa.com/your-receipts/
it says "We didn't find a match."
(Is the above site no longer working, or is it useful only for already flown segments?)

Thanks again.

AA's IT is ancient and aa.com is bad at a lot things, it is not that unusual to not get a reticketing email. So that in and of itself doesn't mean anything is wrong.

I booked a new award ticket yesterday and never received the ticketing email, for example.

If the phone agent confirmed your new ticket number then I really wouldn't worry.

And I'm not familiar with the "your receipts" section at aa.com, no idea if that works or not, however you can try the refunds site at prefunds.aa.com and see what shows up.

Thanks again, to JJeffrey.
Update 2: The email with the new ticket receipt finally arrived, after a second phone call to a different agent.

Ask the agent to re-send you the ticketed itinerary via email. Also, your reservation on AA.com should show "ticketed" or "on request" - depends on that.. if ticketed, then you should be fine..

I had a very similar problem last month. Wife and I were flying LIN-LHR-JFK outbound with a return in December (JFK-MXP). While we're US-based, we have a home in Italy too and pricing is better ex EU than ex US.

Our LIN-LHR segment was delayed and BA rebooked us on a later BA LHR-JFK flight (our original flight was on AA metal). When they did that, they reissued the ticket om BA ticket stock (125 as opposed to 001 for AA). Miles (and Business Extra - RIP) didn't post quickly but did eventually. I did have to submit a new BE request for credit using the 125 ticket #. It took a week or so but everything eventually fell into place.

When you pull-up the reservation for the ba flight in the ap does it show a ticket number and does the ticket number match what aa gave you