Oh!
I thought the problem was when a plant not yet in the database at all, was added into a moderation queue twice (before either proposal was approved into the main database).
In other words, a way to search the moderation queue for more than one entry with the same name. I was also assuming that the database did not update instantly each time a proposal was approved - as if there was a batch process that only ran occasionally.
So ignore the idea. "Assumption makes an ass of me and umption."