Not entirely sure how this one spreads within a game once it's present, to be honest. If the affected lots and sims are removed and the player is able to purge the counter item from DCCache and DCBackup -- Method by Mell for the first one or rebuilding the entire dbc collection as you are doing instead -- then it should no longer exist in the player's game to return again or spread on to others.
http://sims3.crinrict.com/en/2011/01/tutorial-how-to-get-rid-of-unwanted-custom-content.html
(near the bottom of the page)
The answer is I believe you have potentially affected other players' games who have already downloaded your lot and placed it into their game, but it's really up to the player to inspect their downloads no matter what source they come from. You are just as much a victim of this file as everyone else is/was and I think everyone would know you weren't being vindictive in any way by not realizing it. The mistake I made was that the sim that was carrying it in my case was from a colleague at NRaas so I skipped the Custard step and just trusted that it was already clean. That's not going to happen again. And yes, the sim's mere presence in my game folder affected my long running legacy game, hence the AHA! 2am moment that @ZeeGee remembers my reporting when I was finally able to get rid of it. My game has been free of it ever since.