Secrets is packed with details not likely documented anywhere else, certainly not to this extent. The biggest eyebrow raiser of all is that Windows 95 fudges the free system resource numbers. You get the idea. A complete listing of the goodies would fill several pages. There's one drawback to Pietrek's approach, however.
Secrets is almost entirely descriptive, and it sometimes leaves the reader to draw conclusions.
For example, Pietrek talks about the mechanisms for locating DLL-resident routines by name or by export ordinal. He says it's more efficient to use ordinals instead of function names when establishing linkage between an .EXE and a .DLL, since no system memory is needed to store the list of names. Given that programs are often used with the wrong .DLLs in the real world, this can lead to disaster. Secrets is an excellent scientific treatment but offers little advice on application engineering. Windows 95 like a walnut.