Perhaps it's a common myth, but I believe that the Denise revision occured at the same time as the ECS Agnus. It was offered to us when we had our A500 upgraded, but we didn't get the Denise upgraded. Whether it technically belongs to the ECS upgrade or not, I can't say (as I was not a dealer). But I have read that the Denise upgrade is a part of ECS and have always believed that, whichever version is true.
There has been some discussion in the past about whether games are ECS or OCS and I always contend that any game that requires 1meg chip is ECS since that version of Agnus was the first to achieve this (and you can't play say, Dungeon Master, on an OCS machine).