I did eventually get them to release because I served them with a legalnotice - it said that if they didn't release it in 90 days, the rights would revert back to me.
CGGT reserves the right to amend the provisions of this LegalNotice at any time, once it is changed, CGGT will post it in a prominent place to notify the visitors in time.
A developer might put a collection of re-formatted datasets online, but without an explicit license or legalnotice - meaning others won't know whether they are allowed to reuse them or not.