Now that's what I call a comprehensive answer! Thanks everyone. You really know your stuff.
What it was - I've got a real Amiga 1200 and I've already got all my fave classic games in ADF format, but I started wondering if it was worth my while getting the AGA versions instead wherever possible. You've now convinced me it's worth searching a bit harder to track them down. There's no need to settle for second best when everything is free.