There is, in short, no good answer to this.
With regard to the Fulvia, there is another website/forum <http://lancisti.net> where most Fulvia discussion in the US happens, but is oddly unlinked to any other locations. There is also Huib's forum and his excellent inventory of factory materials. It would be nice (very!) for all of this to be centralized. Given the spread out nature of things these days, a central listing of available information would be a positive first step. This could be supplemented by a detailed indexing of information, or threads, perhaps which could be posted on your own site (perhaps)?
The same issue came up on Aurelias. Info was either non-existent on the web, or scattered all over the place. First off is Paul Mayo's excellent workshop manual, where he has tried to compile all the maintenance tips and directions over many years. But it does not keep up with the web. Hard copy only.
Some 15 years ago, surprised by how little Aurelia restoration info was on the web, started posting info on a restoration on a website. This has grown into a more comprehensive Aurelia website <
www.lanciaaurelia.info> where a lot of information is posted both on pages and a long, but unindexed (ouch) blog. There is some information on ASTs, Parts books, tech info, but does not track all maintenance matters, nor all the ASTs. There is a listing of suppliers and of different information sources. Many ASTs were reprinted by James Steerman some years ago, again hard copy only. Again, information is scattered, and difficult for those who are not fully in the know. I suspect this hurts Lancia appreciation in the larger picture: its hard to get a handle on all the information, and its likely some owners and their cars suffer.
Factory copyright is not a critical issue, as this material has been in the public domain for many decades now. However, coordination among all the players and different groups/forums/publications is a big issue. And, as you say, the long threads which can be difficult to peruse, or even can be lost, is also a concern.
Hope this helps.
Geoff