If you read the thrawn trilogy back in the day, or maybe it was was the rogue squadron books, astrommechs have a memory reset that normally happens during maintenance , Luke refused to ever let Artoo get reset. In the past though Artoo has been reset (multiple different owners) he also has a particular personality quirk that he always ends up back in a position where he’s “operating outside normal parameters” or some such bs.
Luke liked Artoos quirk so he encouraged it and preserved Artoos personality by preventing that maintenance
Canon typically is written after scripts are to fill in back story, his beeps and blips were entirely made because George Lucas was/is a technical guy and made his career out of incorporating new fx techniques