Update...didn't work out as I wanted but thought my experience may help someone else..

Had no joy from BAMissingAvios... here's the reply

Dear Chuckstar

Thank you for your message.
I am sorry to hear your travel with American Airlines was disrupted and you were unable to board your original flight. Please accept my apologies.
When travelling with any of our Partner airlines, details of passengers and flights are held in the programmes run by that Partner airline. For security reasons, we are unable to directly access their data if there is a problem with a claim. Also, I'm afraid the decision to award Avios for Partner flights is not made by us, but instead by each Partner; it is at the Partner's discretion whether they allow for your original flights to be credited or not.
However, we are able to contact the relevant airline direct with any additional information and request a review of their decision. I can see from our records, your claim has already been escalated to American Airlines for their further investigation and advice. Unfortunately, we are unable to take any action until we receive their response.
I understand how frustrating this can be and I am sorry for any inconvenience. As soon as the responsible agent hears back from American Airlines, they will contact you by email from your designated case reference XXXXXXXX.
I am sorry I could not be more helpful on this occasion, but thank you for giving me the opportunity to look into your query.

Warm regards

D
Executive Club

I then received a reply from BAEC ...

Dear Mr Chuckstar
Thank you for requesting Avios and Tier Points for your original flight on 4 January 2018
We understand how disappointing it is when flight disruptions mean you're unable to complete the journey you originally booked.
If we re-route you from British Airways flights onto another carrier, we're happy to credit your account for your original flights.
We're always looking at deepening our relationship with our partners so we can offer you a more joined up service, but there are some areas where our policies are not the same. As you may be aware, the decision to award Avios for partner flights is not made by us, but instead by each partner.
I’m sorry to say American Airlines does not award Avios for your original flights, so we are only able to credit your account for the flights you flew.
I'm sorry I couldn't be more immediately helpful, but if there is anything else I can help with please let me know.
If you would like to contact me again about this case please click on this link:
XXX Best regards
W
British Airways Executive Club

Undeterred I emailed AA to see if they would help me out...their website was not particularly user friendly in this aspect and I have not received a written reply, instead it appears they have credited my Amex account with £60 - I'm guessing thats the fare difference.
So no ORC on a AA ticket !