Sitecore Item Version Count Mismatch
I recently came across an issue in an upstream environment where an item showed as having 2 versions, but only one appeared in the dropdown.
To replicate the issue, I packaged the item up and installed it on my local. Voila. The 1st version appeared in the dropdown list.
Issues like this can arise due to index corruption.
The quick fix is to run a reindex in the affected environment (master and web).
To put the issue to bed once and for all, check your Sitecore and Solr logs to find the root cause.
Keep on BUIDLing.
-MG