I think it has already been answerd here for me, but i will use my example to help me make sure i understand.
Basically we have the Sims 3 Base Game which was from Retail, when i installed it it went into my origin games list. I now want to get expansion packs, and they are cheaper at my retail store than the origin store. So if i buy it from retail and install it will it work?
Yes.
Only thing you can't bring into the mix is the Steam version.
Also beware this issue: http://answers.ea.com/t5/The-Sims-3-Into-the-Future/IMPORTANT-DLC-Compatibility-Alert/m-p/1694095
