Own partial set from sims3 store

I wanted to know what happens if you already own part of sets that you had bought individually and now want to get a set that has it in, for example I already own the casino from the sims3 store but I now want to buy Lucky Palms which I did not realise included this in the gold edition, which I would prefer more. I do not however want to end up with double ups or worse buy for the same thing twice. Any ideas, Thanks.

Another example is I bought the magic set to get the book of spells but have now seen a compilation - best of 2012 - which I would love to buy but again I don't want to double up or pay for something I already have bought. Thanks.