SHA512 without salt

I've got a group of hashes that appear to be SHA512 (start with $6, have the number of rounds listed in the $rounds=5000 format) but don't have a salt. -m 1800 doesn't work and I've tried to tweak the hashes a few different ways but so far no luck so I figured I'd check with the community.

Redacted Example:  $6$rounds=50$XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

Thanks,

Matt