To the best of my knowledge, although Adobe claimed their activation servers were being shut down, the activation process, "FNP licensing service", is still running in their CS-2 products. So, while the original SN# provided, may still work on the original wave of download packages, it likely won't work any more, especially if you're connected to the web.
So, the moral of the story is, "thou hast snooz-ed, and thou hast lose-ed"....
I don't think that was ever an official promotion, so your results may vary. Adobe may have patched this.
Not only was it, "not an official promotion", but it was an overt, massive screw up, on Adobe's part. The "free" downloads have long been taken down, and you need an Adobe ID & account to log in. When these downloads were first put up, Photoshop Elements 5 was on the list. The odd part about that is, PSE-5, never needed activation in the first place. It was always a serial number entered program. As such, you could always put it on as many computers as you liked. As of PSE-8, Adobe abandoned, "the honor system", and all PSE variants,. 8.0 and later, require activation.
So, my best guess is, Adobe invalidated the first serial numbers in newer downloads, and you now probably need your original CS-2 serial number, to receive a non-activation download of their CS-2 product.