Authorize.net recurring payments are not received show in Civi IF contact is merged or end user deletes first contribution

When A.net recurring payment is received the a.net getIDs function checks to see if the contact_id, contribution_id & subscription number in A.net & in CiviCRM all match. If not the payment is sliently never recorded in CiviCRM.

Unfortunately there are valid reasons' for the contact_id to change (de-duping) and reasons that seem valid to the end user for the original contribution id to be deleted (they entered two by accident & delete the wrong one) which leads to no more contributions ever being shown in CiviCRM (fortunately our customer has been doing some pretty thorough reconciliations!).

I would suggest that once the contribution_recur has been created in CiviCRM the combination of civicrm_contribution_recur.processor_id (generated by A.net) & civicrm_contribution_recur.invoice_id (which should be the same as the invoice_id of the first contribution) would be a more robust & still secure check to do.