We noticed if you use the search functionality on an iOS device you can still access old deleted iMessages.
In order to reproduce, delete an iMessage. Then go to the search screen by tapping home button twice (you should make the search from the general search screen, not using the search section in the Messages app). Search a word in that deleted iMessage. You will see the message in the search results.
Yeah, pretty old news tbh. This happens because Spotlight's index has indexed those texts from when they came. To clear the index, go to Settings > General and uncheck Messages.
In order to reproduce, delete an iMessage. Then go to the search screen by tapping home button twice (you should make the search from the general search screen, not using the search section in the Messages app). Search a word in that deleted iMessage. You will see the message in the search results.