I have had a response from Amex to my enquiry about the £5 credit knocking off 5MRs

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Dear xmassheep,
Please do not worry; I will take care of this for you.
Whenever a credit is applied on the account, systems consider it as a return to the merchant and deduct the points accordingly.
As a corrective action, I have applied 15 points on your account to cover the point’s deduction due to three Shop Small credits.
If you receive any other Shop Small credit, please write back and I will make necessary correction again.
I hope you are happy with my action. Your membership is important to us and we look forward to enhance your customer experience with every interaction.
Sincerely,
XXXXXX XXXXXXXXXX
Email Servicing Team
American Express Interactive Services
I have just checked and it has landed in my MR as 'Goodwill credit', so some of you should be in line for a few MRs given how much you've managed to use this promo