Att Jay Garrick var en komisk karaktär av Earth-2 ... inte en riktig person på Barry Allens jord-1.
Per Wikipedia
In 1956, DC Comics reinvented the Flash character, giving him a new costume, name, and background. Named Barry Allen, he was completely unrelated to Jay Garrick. In fact, Garrick never existed as far as the new books were concerned. Barry Allen's first appearance shows him reading a copy of Flash Comics, lamenting Garrick was "just a character some writer dreamed up".
Detta anges faktiskt på samma ComicVine länk:
He [Barry Allen] also had a love of comic books, his favorite hero being the Flash ( Jay Garrick).
Så småningom:
In 1985, DC Comics merged all of its fictional characters into a single shared universe. Jay Garrick now shared the same world as the new Flash.
Så, som svar på din fråga, fanns de faktiskt inte i samma univers / jordvarianten tills mycket efter att Barry Allens Flash skapades.
Du kan läsa om den aktuella "statusen" av Jay på Wikepdia-länken.