I actually think this is a somewhat Beatles myth.
Before Martin even met the Beatles he would have known the direct correlation of tempo/pitch to the tape speed. During Revolver he would have learned this in more detail such a specific line frequency changes to change pitch to certain keys because you have to be able to overdub hard tuned instruments onto pitch altered backing tracks (not sure they did that specifically though) and those altered backing would HAVE to set to some standard pitch even if not the original one. Voices are different you can sing in relative pitch to any speed backing track.
So with "Strawberry Fields Forever" Martin would have KNOWN that the lower pitch and lower tempo take 26 could have been sped up to somewhat match the original take 7. I suspect that was always the plan. They were NEVER going to release "Strawberry Fields Forever" in it's slow incarnation like we hear on bootlegs it was always going to be sped up somewhat.
The "miracle" was really that both version's could be matched so well. The "maybe, i'll try" became an "OMG, it works!" moment.