Identify NB images that only have one copy

We are migrating to two new Data Domain appliances.  As a result, I have been duplicating my long-term retention images from disk/VTL to the Data Domains.  I keep the two Data Domains in sync so anything written to one gets duplicated (via Netbackup) to the other one.  I want to make sure I didn't miss duplicating any of the images so is there an easy way to identify images that currently only have one copy?

Thanks, Frank