I originally bought the "cheapest" option when it first came out, which is HL2 only. (I think it was called the "bronze" package). I wanted to upgrade so that I could buy HL - Source, and was told "nope, that's not an option - - you steam registered the bronze package, and if you want HL Source you have to purchase the whole "silver" option (or higher) and obtain a new reg. number.
In my opinion, this is bad business. You should be able to add stuff if you're willing to pay for it, without reinstalling the whole thing all over again, just to get a new "registration" number. Valve screwed the proverbial pooch on this one ...
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I like Pop Tarts
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