Originally Posted by
bat39
Yeah, the Bruce-Selina marriage was something retroactively established as taking place on Earth 2 in 1955.
Kathy Kane was introduced in 1956 and appeared in stories till around 1964 (sometime before the 'New Look' retool of the Batman books). 1956 is now being considered the starting point for the Silver Age Batman as well it seems (in fact, the Silver Age Batman Omnibus has the cover from the first issue featuring Kathy Kane as its cover). So she is very definitively a Silver Age character who existed on Earth 1.
However, an Earth 2 Kathy Kane was later also established as existing retroactively, and she was around in 1955 (appearing in the same story which revealed Bruce and Selina's marriage). She also appeared later in a story where the Earth 1 Batman ended up briefly on Earth 2 and teamed up with Dick and Kathy.
I just thought its an interesting coincidence that the first major divergence in Earth 2 Batman's life, compared to the Earth 1 Batman's, was his marriage to Selina in 1955. And 1956 is now considered the start of the Silver Age/Earth 1 Batman, and the Silver Age DCU in general.