This article is from the Dr. Pepper FAQ, by Christopher Flaherty with numerous contributions by others.
It sounds pretty obvious once you know it, but I never would have
guessed until someone pointed it out to me: The original title of Sgt.
Pepper's Lonely Heart's Club Band -- one of the Beatles' most popular
albums (and consequently one of the most popular albums period) -- was
Dr. Pepper's Lonely Heart's Club Band! Wild, huh? When I asked the
fine folks at rec.music.beatles for confirmation, Jim Demes
(email@example.com) wrote me on September 29, 1998:
According to BEATLESONGS by William J. Dowlding: "The album was
originally titled Dr. Pepper's...until the Beatles realized an
American soft-drink company had rights to that name." Dowlding got his
info from THE BEATLES A TO Z. (1980)
Whether or not the Beatles were fully acquainted with the soft drink
before they began work on Sgt. Pepper is still subject to debate. But
bottles of Dr Pepper have been spotted in the Let It Be movie, so they
had definitely seen the light by then. Imagine what else might have
been if only a few letters hadn't changed . . .