I believe your theory is reasonable.
asrestore has an option to skip restoring a record if it exists already… (refer to the -u option – the first one on the asrestore write-policy-options doc) that would make sure to only restore records that haven’t made it to B. You may want to disable XDR temporarily while doing this to avoid race conditions with records that may be ‘in flight’. I think those options and details are discussed on this article: How to Migrate Aerospike from one Cluster to Another.