There is lots of discussion regarding preventing duplicates on this issue: Prevent duplicate sibling contact capture · Issue #9601 · medic/cht-core · GitHub
The initial focus is on preventing duplicate contacts, but we are trying to implement it in such a way as to be able to be naturally extended to reports in the future.
Most relevant to this thread, though, is that it is still going to depend on the existing report not being purged from the device. 
I do wonder if it is possible to setup your purge config to always leave the most recent copy of any purged form type. 
If not, that may be a possible feature to pursue adding…