If you're good enough at digging through the internet, there are some chronicles from 2012/13 about the Battle of Caldari Prime that explain this to an extent, or at least use the number in the lore to justify its presence. Some of it is in the fiction portal on the main site, but there are others that disappeared somewhere, and i don't know where.

If i recall correctly, when the older generation of clones were created, they used Sleeper implants to make them so that consciousness can be transferred from one clone to another in a way similar to Capsuleers, but more efficient and tailored for infantry use. Some troopers were unlucky enough to have their implants malfunction and have their minds taken over by the sleepers, not unlike Jamyll Sarum; except instead of going into a raving seizure-like fit, they went almost insane and went on mass killing sprees, attacking both friendly and enemy forces. Before dying due to wounds suffered at the hands of the people they attacked or by their own, they would write the number 514 in their own blood before dying completely; their consciousness destroyed by the sleepers, thus rendering them unable to be revived in a new clone.

This was colloquially known as "Going 514".