In the Condensed Rules and the Enchiridion of Elucidation they mention rule changes made after the First Edition from Trail of Cthulhu.
Is there a resource that list all the changes? I could find some of the changes on those two documents, but I want to know what effectivelly changed.
It's not much of an answer but there has only been one edition of Trail of Cthulhu. Some rules changes have crept in via scenarios and sources books, for example magic in Rough Magicks or auctions in Bookhounds. The changes mentioned in the Enchiridion however refer to rules introduced in other GUMSHOE rule books or in the System Reference Document. However, to quote Robin Laws on this:
It’s not The Esoterrorists with the IP elements scrubbed out, but rather the set of components you need to build your new game on the GUMSHOE chassis.
Each GUMSHOE rulebook is a separate game system. There is likely to be a 2nd Edition version of Trail of Cthulhu at some point and it will probably include some of these minor rules changes.
The biggest change to "typical" GUMSHOE that Trail of Cthulhu has is the addition of a Sanity stat separate from Stability. Stability, like Health, shows how someone is doing right then; Sanity represents how close the character is to permanently losing it (in fact, this change separates Trail from all other X of Cthulhu games, since none uses two stats that way).
Cthulhu Mythos skill has an additional mechanic different from other Investigative Abilities, too. A player who is stuck can spend it and immediately find out a horrible truth driving the game - at potentially significant costs to Stability and Sanity.
I'd argue that Trail is a pretty stripped-down game, sacrificing mechanics for a larger list of skills. Since it is a pretty early game - as Steve says, the earliest one that hasn't seen a new edition - a lot of the changes in thinking about how to play GUMSHOE are sort of unofficial.
