User blog comment:Supahbadmarine/Official Canon Policy/@comment-3341288-20130222153207/@comment-9465750-20130222195406

Well, as for loyalist traitors, individuals and small groups are OK (but they should all die till M33, exception would be a dreadnought)

As for non-canon, fan faction empires, if they are located on the brink of the galaxy, the halo stars or out of the astronomican reach, then they can have around 500 planets