Not sure that completely answers my question but I was curious as Heimlich and Co. won the SdJ but was later released as Top Secret Spies. Both have the stamp.
Being somewhat of a SdJ collector, I believe TSS has that stamp because it was an English import of Heimlich and Co.. ie: HC wins the SdJ, Rio Grande translates it and imports it.
I haven't played Keltis or LC:TBG, but from comments above, they look to be different in some respects. Jay had to make a business decision on what might sell more games in North America: a SdJ stamp on a game no one had heard of before, or to use the familiar branding from the Lost Cities card game. I recall hearing this on a podcast I believe, but RGG had a few partners that were behind the LC:TBG, before Keltis won the SdJ. They pulled out, and went with the marketing pull that works best in Europe: the SdJ stamp.