Given the whole "licensed not bought" thing with samples, would buying a copy on eBay be sufficient?
EDIT - found an old manual for another eMagic library and the licence is "non-transferable"
You said above you already own a copy of it (and were using it), but have no proof of ownership - no receipts, no media, nothing.
If you buy a second copy of the media, you now have proof of ownership, because you can show the disks. That's as good as you're going to get, because there is no "licence in your name" or anything like that that came with these libraries. At best there might have been a serial number, I can't remember without going to look at my copy, but I doubt Apple would be able to look that up for you now. Remember, the original company that licensed that material does not exist anymore.
So it's not about officially licensing old content, it's about being able to prove, as best you can, that you have legitimate access and rights to use that material. Think of it as replacing your lost media, not buying an unofficial non-transferrable license.
Now - not a lawyer, obviously, but if that isn't good enough for you, then there is nothing short of you finding a purchase note/invoice for that library that will reassure you...
Given that a lot of these samples were, according to the pamphlet, "sourced from various HipHop producer friends", it's possible that the legality of much of the content is questionable anyway (unless all producers had to create original content only and sign contracts saying they were all their own work, which is certainly possible), which is why Apple never took it on and integrated it into Logic, unlike the Analog/Digital libraries, which were done in house. Take that as you will...
Last point - given how concerned you are about proving sample library licenses, it's strange to me you would have bought a sample library and not kept records of this, and the original media, for exactly this reason. Are you *sure* you bought, or had, this library? If you never bought it, or never had the disks, then I'm pretty sure you wouldn't have got it legally (like I say, this was never bundled without packaging with other emagic products). It all seems a bit weird.
Like I say, if you can provide examples of filenames from this you've used in your commercial work, I can look them up to see whether they came from Xtreme Hip-Hop, or whether they were from the Logic Studio factory content - and if it's the latter, then you can rest easy.