I agree! Any sim your game creates is 'yours' and fair game to upload to the gallery without crediting anyone (adoptions, NPCs, etc!). If you downloaded a sim another simmer made from the gallery and completely redid their hair and clothes (a full makeover!) you should probably still give credit to the original simmer -They did make all the bone structure and body!
As for lots; I'm assuming you're talking about editing lots that come already placed (by Maxis) when you start a new game. For in-game lots you've remade or edited most builders just add a #reno tag (renovation) to the build.
If you're talking about editing a lot that you download from the gallery and would like to re-upload with your changes, you can find the original lot in your "My Library" page of the gallery. If you click on the picture, directly at the top, it will say by:Username <-That's who you'd credit.
Hope that helps!
