I conducted more internet research on the Federal requirement in the U.S. It appears that the Food and Drug Administration (FDA) was the “responsible” regulator until the CPSC was stood-up on May 14, 1973; three commissioners had to be nominated, with routine FBI investigations about their partying as teenagers; confirmed by congress; and then to actually meet in D.C. However, on May 10, 1973, the FDA first proposed the Federal bicycle regulations, open to public comment (dealers, distributors, manufacturers, retailers, and their associations); 4 days later the CPSC took over, and hit the ground running.
Over a 14 months later, on July 16, 1974, the CPSC issued a final rule, but allowed almost 6 months before it went into effect as “adequate time for redesign and retooling”.
Bicycles (non-compliant ones) were added as Number 12 on the list of “Banned toys and other banned articles intended for use by children”.
(12) “Any bicycle ... that is introduced into interstate commerce on or after January 1, 1975, and that does not comply with the requirements...”.