It's certainly possible that he started to put the pickup further from the bridge and changed his mind. I read somewhere that the earlier ones had the pickup closer to the bridge, but with no build dates I don't know how that was verified.
From Bud, about his own instruments:
During this time, in about the year 1948, I was making a guitar for a very excellent Hawaiian Steel Guitarist, Ray Morales. Ray had a very extensive ability on the Steel and upon occasion, played a lot of rhythm on the bass strings. He wanted a guitar that would give him more depth of sound on the bass strings. In an attempt to find a way to have the steel guitar give more depth on the bass strings, I took a pickup, outside of a guitar, and placed it in various places over the strings. I found that putting the pickup about six inches IN FRONT of the bridge gave much more depth of sound from the strings. Upon discovering this result, I changed all my pickups on my electric basses to some six inches from the bridge. This is still prevelant in basses today.
Also, while "fooling around" with this pickup, I found that slanting the pickup so that the polepiece would be farther from the bridge under the bass strings and closer to the bridge under the treble strings gave much more depth to the bass strings while not hurting the treble sound of the higher strings. I have a picture of Sol Hoopii holding one of my guitars in 1953. The guitar was my "slanted" pickup. With Sol passing away in 1953, I certainly have proof of being the first to "slant" the guitar pickup. You will note that most every guitar now has a slanted pickup (near the bridge).