Chris,
CW> I don't have any lines in my configuration file for any of the servers,
CW> how can I tell what the default protocols are?
you may want to add
log file = /var/log/samba/log.%m.%R
to the "global" part of your smb.conf.
The %R gives "the selected protocol level after protocol negotiation.
It can be one of CORE, COREPLUS, LANMAN1, LANMAN2, NT1, SMB2_02,
SMB2_10, SMB2_22, SMB2_24, SMB3_00, SMB3_02, SMB3_10, SMB3_11 or
SMB2_FF."
This will at least give you information about the actually used
protocol for every client. A bit "the other way around", but it might
help.
Michael