Side one of the original LP is occupied by the 21-minute title epic track, beating both Genesis' "Supper's Ready" and Yes' "Close to the Edge" by a year.
Source: http://www.allmusic.com/album/tarkus-mw0000652026
I am not sure what exactly "beating … by a year" means in the context. Does it mean that "the title epic track" is better than the two mentioned LPs that were released one year later after Tarkus.
To beat something|someone by a {unit of measure}
means to outdo it|them by that said unit.
The unit of measure could be literal or an exaggeration. You can beat someone in a race "by a mile" and actually beat them only by a few strides. If the race were a 100 meter dash, to beat someone by a few strides is to beat them soundly, and you could be said to have beaten them "by a mile", that is, handily; whereas in a marathon, a few strides is almost nothing, and there you might exaggerate in the opposite direction and say that you had beaten them "by a hair".
In your case, the LP might have been released a year earlier than the others. To answer that requires some knowledge of the context. If they did indeed come out a year later, then they were "beaten" to release by a (literal) year.
