I don't think any of them were cast-offs, just "works in progress". Hendrix wrote by recording EVERY jam, some songs he worked on for over a year or more, you can hear all kinds of stylistic changes in these tunes as they become fully formed. It's one of the most fascinating aspects of having all this stuff reissued, you get to "sit in" with Hendrix and experience a bit of the creative process involved.
Half of the tracks on Valleys of Neptune were recorded in 2 days (Feb 16th & 17th, 1969), more material from the Olympic sessions was released in the Experience box set. Hendrix was at an absolute peak during this year, his level of creativity was staggering.
The very next day, Feb 18th, Hendrix started a 2-night engagement at The Royal Albert Hall. Those concerts have attained mythical status over the ensuing decades and the last time I heard, they are next on the release schedule for the Hendrix estate.