Hoping this is the right place to post this:
I have a few lots that I want to upload that use custom wall coverings by plasticbox, yet they aren't available in their downloads, but rather lots that they have uploaded and packaged the wall coverings with. Would I be able to upload the lots if they use these wall coverings? If so, should I package the wallpapers with the lots even though they don't belong to me?

Just my opinion - I would suggest it is probably okay, since you can link the original lots. I think Plasticbox is still around, though not with TS2 - you could ask her!

Okay then but I'm not sure where I'd ask her. I could PM her but she hasn't been active here since 2016.

I would say upload and give proper credit, which you have to do to upload to MTS anyway. I don't think Plasticbox was ever really fussy about this, and they moved on to the newer games long ago, so they're probably not going to care about a few walls they made for TS2. And if indeed they haven't been active in three years, it's kind of silly to worry about it at all. IMO, anyway.

I'll do that then. The house is ready to upload. Should I package the wall covering with the lot?

I would. I will sometimes leave CC out of a lot package if there's a lot of it, so that people can more easily choose whether or not to use it. Most people aren't going to fuss about a couple of walls and, if they are that fussy, they can tell Clean Installer not to install them and then just replace them with something else.

I would include the wallpaper since the only other way to get them is to download the lots that contain them (I'd also make sure to point a link to the original builds). I enjoy downloading people's lots but there's not much point if I have to download stuff I don't want just to make it complete.

Yes, include it but just give credit and link to the lot is originally from. I had to do this with some windows triciamanly made and packaged with her lot but wasn't a stand alone download.

I'm not sure why you would need to link to the lots, since you'd already be crediting Plasticbox for the walls in the CC list, but if it makes you feel better...

It's part of her TOU actually...

To link where I found the wall covering?

Well, it says to link to specific uploads rather than the user account. Usually, that's the sort of language used if you upload a set of something, like a set of walls by itself. They would like a specific link to that set of walls, not a general link to their user account. Not sure if that applies to something uploaded with a lot since you can't really directly download the walls from the lot, only extract them from a lot package. I'm also not sure it entirely matters if they're no longer active, but I'm not up on the latest MTS rules for uploads, since I don't really upload here anymore.

I would say do whatever makes you most comfortable. Unless something has changed with the lot upload process here, you have to provide a link to each piece of CC you included with the lot. It's part of the upload wizard. So, you'd simply make the link to that upload. I don't think you need to do any separate credit/link to the lot that contains the walls. Like in the upload text, I mean.

Creator Guidelines say you need to provide a link to the upload, not a creator's profile. And since Plasticbox allows her stuff to be included you should be good to go!