It's my understanding that Fender never applied a Butterscotch color to their guitars in the early 1950's (or the 60's or 70's for that matter).
As I understand it the Butterscotch color is result of oxidation and other slow chemical changes to the Blonde finishes that Fender was putting on Telecasters.
I have read that Leo Fender, when asked basically the same question, replied that they were experimenting with an acetone based lacquer in those early years. His theory was that the acetone was responsible for the color shift toward what we now call Butterscotch.
In the mid 1980's when Fender decided to start replicating the early Telecasters (52RI) they took a look at the fact that collectors preferred the Butterscotch color to the comparatively tame Blonde finish that originally came on the instruments and formulated a true Butterscotch finish for the Re-Issues. That is why the '52 RI's have that really intense peanutbutter color to this day. It's a marketing thing.
In fact, it seems that some players and collectors actually believed that the old Telecasters came from the factory with the Butterscotch color. Of course they didn't...and what they were/are seeing is what some refer to as 'Bar-Tan' (years of oxidation resulting from exposure to cigarette smoke and other pollutants, ultra-violet...etc.)
A similar color-shift can be observed with Fenders 'Olympic White' which, thru the same oxidation, darkens and mellows to a nice amber yellow color (aka Banana Yellow).
Everybody loves the Butterscotch color; including me. But it's not what Fender put on their guitars back in the day. Remember that blond furniture was REALLY big in the late 40's and early 50's.... Leo knew that and used it as a marketing technique. Smart guy that Leo.
Louie Seven