Autosave will save the project exactly as it is when it saves, in full and intact. If the autosave didn't have all the sequences, it's one of three possible reasons, in descending order of likelihood.
1. The sequences are actually there, you just need to open them
2. The sequences were deleted by you prior to the auto save.
3. The crash corrupted the autosave files. (This is a very, very small possibility, though, seeing as it appears to have happened to all five autosaves, not one of which was actually 'open' at the time of the crash.)
You should be able to see the date\time of the autosave prproj file when selecting one. It is good practice to set the autosave prefs to save more often and keep more versions.
It turns out the sequences were not missing from the project. However, they were not showing up in the timeline area where expected. Once the missing sequences were discovered in the project list, double-clicking on them would make them appear in the timeline as expected. It was the first two sequences that were missing from the timeline area. It may be relevent that there were two new sequences created since the last manual save. So the total number of sequences in the timeline area remained at 4, but should have increased to 6 at the time of the autosave, and all 6 were visible at the moment the PC crashed.
The number of open sequences is actually not stored with the project, but holds true across projects.
So if you close project A with 4 sequences open, it'll open project B with 4 sequences open, no matter how many were open the last time you worked in project B.