421 is an encrypted talkgroup, have seen it used for a year. 1537 is used for some sort of station alerting for Bethany FD, I believe. 1656 is used for some sort of school activity, perhaps PC schools.
2001 is some sort of station alerting for OCFD, I believe for when there are medical calls. 2047 I've seen used for OCFD to patch with other systems/frequencies.
I monitor the core simulcast layer mostly, have not seen any activity on Unitrunker from groups 1919, 1537 & 657