When the composer of a given piece of music is not the one to write up the sheet music, the key/time signature/etc. are up to the discretion of the transcriber. In some cases, they do a terrible job, leaving anyone looking at it confused or annoyed trying to read it as they chose to transcribe it. I suspect that some companies that publish this material use computer algorithms to analyze and transcribe but I don't have any evidence for that claim. When something is labeled "official", as you mentioned in a comment, you would really need to determine in what regard it is official. Jimi likely didn't sign off on it... It may just be indicating that it is released with the proper licensing.
From what I recall of this song, it wouldn't exactly be in a single key, ie, not all of the chords can be derived from a single tonal center/key. In particular, the E7 chord contains a #9, which cannot be derived from any naturally occurring any key.