No, no, no, no. Here's what I've done in FS2 so far:
Finished main campaign
Played Derelict up until the third-from-last mission
Updated to 1.20 in order to try out multiplayer
Finished Derelict
Went to admire my stats - and found they only reflected my progress since I had updated! Since my progress through the campaign hadn't been lost, I didn't notice anything wrong until I went to look at the list of medals and saw them all gone.
Not only was my score lost from pre-1.20 playing through Derelict, but my rank and slate of medals were lost from the main campaign, which I had already completed.
I don't suppose it's possible that playing multiplayer, rather than updating, could have wiped out my stats? All I did was clone a multiplayer pilot and update to 1.20. Now my single-player pilot is busted down to Ensign!