This answer addresses your second question, regarding the specific case of SGA 5. In short: the contents of **SGA 5 Exposé II** can be found in Deligne's "**SGA 4 1/2**". Also, see my other answer about the original Exposé. According to Grothendieck's "Recoltes et Semailles", SGA 5 was totally butchered by Illusie, in a combined effort with Deligne so that it looked useless in comparison with SGA 4 1/2 (which wasn't a true seminar, and stole some of the missing exposés from SGA 5). This is also the reason why SGA 5 was the last to be published. About the lost exposés: - There was a group of introductory exposés about the relations of SGA 5 to other contexts and about the philosophy of six operations. Illusie had them, but he sent them to Grothendieck and I don't know where they ended up. You can read more about them [here][1]. - Exposé II, as I said earlier, was reworked by Deligne and included in his volume about Étale Cohomology. The original exposé is kept at the IHÉS and can be read online (see my other answer). - Exposé IV, about "The cohomology class associated with a cycle", was going to be redacted by Deligne, who instead included it in SGA 4 1/2, chapter 4. This theme also included an étale version of homology, with a formalism about the homology class associated to a cycle. According to ReS, these ideas were published by Verdier in an article with the same name. You can read it here: <cite authors="Verdier, Jean-Louis">_Verdier, Jean-Louis_, [**Classe d’homologie associee à un cycle**][2], Astérisque 36–37, 101–151 (1976). [ZBL0346.14005](https://zbmath.org/?q=an:0346.14005).</cite> - Exposé IX was about Serre-Swan modules and was published elsewhere by Serre (Linear Representations of Finite Groups). This one was published by the IHÉS and can be found in some libraries. - Exposé XI was called "Computation of local terms" or something like that, and was substituted by exposé III-b. Apparently, Bucur wrote it and sent it to Grothendieck, who somehow lost it. - There was also a last exposé about open problems, which Grothendieck talks about in ReS and which notably contained a conjectural "discrete Riemann-Roch theorem", later referred to as "Grothendieck-Deligne conjecture" and studied by [MacPherson][3]. He also mentioned a trace formula modulo $p$, which was treated by Deligne in SGA 4 1/2. [1]: https://mathoverflow.net/a/460231/385781 [2]: http://www.numdam.org/item/?id=AST_1976__36-37__101_0 [3]: https://www.jstor.org/stable/1971080