I know there are many threads already about the 1983 mule but i thought this one needed a new post. I have kept tabs on them for many years and read the rumours on here that they may have been in the annual coin set but have never seen evidence of one until now. There is a set up on eBay now and have a comprehensive reply from the seller.
https://www.ebay.co.uk/itm/RARE-1983-2-New-Pence-in-Unrecorded-Royal-Mint-Brilliant-Uncirculated-Coin-Set/233308601941?hash=item365246be55:g:SdIAAOSwYXVc1C4A