For my packs, I try to avoid overlap as much as possible, while also keeping an eye on what a set needs to "feel complete". I'm working on a village set and a farmstead set now, so your example is apropos. These two sets will share more pieces than my usual sets, because I don't want a user to feel forced to buy both. Both sets will share, in this case, some basic buildings, a hearth, and some very basic furniture. Both sets also will have the "basic" floor tiles, a few trees, and a boulder from my Forest Pack I, because you need something to sit your village or farm on and not having a tree would be wierd. I feel like it would be less ethical to restrict my trees to only that one set, but I also put about 190 hours of work into this village set, so I don't feel too terrible reusing a tree. I aim for at least about 80% unique stuff in each set, but may bend that if it makes the set make more sense to include more from my library. For me it's a balance of making sure my most loyal and awesome customers feel "wow, this is super worthwhile" and someone who's never bought any of my stuff doesn't feel "but why are there no trees?!"...and if I'm honest not repainting a new tree for every pack just to claim it's "new". Cause that last doesn't really add any deep value, and it will also make me kill myself around tree number 843. It is my hope, at least, that the wonderful folks who buy every pack I produce can understand and forgive me for reusing my favorite tree so that new people have at least one tree. Oh! Also! Pick a good naming convention and stick with it, exactly to ensure that people aren't downloading the same asset with different names. "Tree.png" is less help than "NF01_TreeLg_10x10.png"