Thread:Love Robin/@comment-26120048-20170218201404/@comment-366087-20170218211232

Initially it was because Supergirl was on another channel. For the first crossover event they had to utilize Flash using his speed and a device to break the dimensional barrier to end up on *her world.

Since the channel-hop, Supergirl may be on the CW, but her world is still dimensionally different from the Arrowverse and she has to be brought across the dimensional barrier.

Thus ONLY the characters which interact with Arrowverse characters during crossover episodes can be considered Arrowverse. Supergirl herself is the exception because tagging *her* as Arrowverse will only confuse contributors into thinking *her* characters are as well.