When you are in acquisitions if you order from an external source it checks for duplicates. If you order by entering a new empty record though it doesn't check for duplicates. It should check for duplicates no matter how you're ordering (new record, z target, staged file, suggestion)
This is still an issue as of 23.05. A fix would save lots of de-duplication time for libraries who manually enter orders into acquisitions.
We have a newish Acquisitions person who has been ordering during the several month duration of no cataloger. We just hired the cataloger and she's going through the new books waiting to be cataloged. We had several duplicates and because it's been awhile, returning them will be a challenge. I was under the impression that the acquisition module would catch duplicates at the point of entering them into a basket but it seems to not be the case. We would really like this fixed. It makes economical sense for libraries to prevent duplication and since that happens in other areas of Koha, to makes sense to translate it to this application.