when I read the scene, and from seing some of the notes (where that sort of background info was nearly inexistant...) and now seing the complete absence of additional details in the Companion (which I see as a confirmation that RJ left no elaborate notes on the OP objects) pretty much finished to convince me: I think the Seeds are purely Brandon's invention, not something he based at all on RJ's notes.
The biggest clue is this: investing objects with Power then transforming them or translating them into powerful Talismans, often weakening the wizard in the process, is awfully RPG/Game-ish (it's also basically yet another rip-off by the game creators of Tolkien where all the objects of power in LOTR and even more the Silmarillion weaken or bind to them their maker), and completely different in inspiration/approach to RJ's, as with his matrices etc. he was pretty much inspired by physics and science, not by magical principles (at least not occidental. What he borrowed from magic is essentially from Taoist magic).
The whole thing read like fan service and RJ wasn't the type to indulge us with that sort of thing either. And he hated to tie things up nicely with a little bow on top, and this cute parting gift from Rand, giving the fans what they wished that the story itself didn't require and that was never even foreshadowed in any seriously or obvious or obscure way by RJ (the rediscovery of the principles of angreal/san'angreal, I mean) did just that.
That's very typical of Sanderson's books, however.
It's awfully convenient, even the details of the making itself all serves exactly the author's purpose: Brandon put that there, but he of course couldn't have Elayne suddenly make angreal by the dozen for the channelers of the Light, so it became a long process and couldn't be done in the time of war since it weakens the maker "for months".
In the past, RJ had rather been hinting that some ter'angreal and the angreal/ter'angreal were complex technologies. The loss of manufacturing means because of the war was his explanation for the flaws of Callandor. The Access Keys must have been extremely complex too, as when they got lost the Light couldn't simply make new ones.
Elayne was still making only baby steps... struggling even to replicate simple ter'angreal... training rings relying on a single flow to activate (and none of them were quite perfect...), and a technology that was invented a thousand years post-Breaking and which much have been way simpler than very advanced AOL technology. It's even said that her ability doesn't make her very good at discovering for herself new principles (and that I know for sure came from RJ's notes on Elayne), so the whole notion that Elayne could pretty much rediscover on her own without more specific explanations how to translate the seed into an angreal, how to give it a buffer that wouldn't be flawed because of her shabby, wholly guessing amateur manufacturing... let's say the odds aren't that good, and it even sounds very much like a misinterpretation of her Talent as RJ saw it.
And of course I'm still quite mystified by the fact Rand suddenly discovered as if by magic that Elayne had a Talent to duplicate ter'angreal. He never knew that before he showed up with a Seed....
So I'm quite convinced the whole thing has very little to do with how RJ envisioned the making of angreal/san'angreal, if he ever did go beyond the notion that they required advanced technology or principles and thus couldn't be rediscovered, and thus it was pointless for him to world build that for nothing. Of course he probably had an explanation in his mind for their making, which he could give us in a Q&A etc. if he was so inclined, but this wasn't the sort of things he kept notes about. Also missing are all the explanations for the creation of Grey Men, Gholam and so on and so forth... RJ no doubt had ideas for that too, but no formal notes..
For the same reason the Companion is wholly silent on details about specific ter'angreal. It looks like RJ may have thought of true purposes for his artifacts when he introduced each one through the books (some of which are obvious even to us as variants of modern techs, others not quite) but he didn't keep notes on that, because if he wanted a Forsaken or LTT to reveal something about them later, he could make whatever he wished up since it contradicted nothing...). He even kept all his options open when he could - not all objects had a functiona attached in the notes (and none that we didn't already know, except maybe for one or two of Cadsuane's gizmos which, by the way were not given a fancy AOL name in the notes... Brandon must have come up with that too, and the notion that LTT had one, that sort of contradicted Demandred's assessment in WH that at least one was post-Sealing technology invented out of desperation).
