To be pedantic, none of those machines are “servers”; they are all desktop machines.
The 10 and 20 in particular had a much longer lifespan than a lot of folks realize. There were cheap (for the time) upgrades to put quad CPU's and a decent selection of SCSI HBA's, Ethernet NIC's and even some ATM interfaces. I know I still saw those units fairly commonly well into the mid 2000's.
https://en.wikipedia.org/wiki/SPARCstation
That being said, most orgs had little reservations about putting workstations into server roles, including every company I worked for, such as a regional ISP.
the "SPARCServer 20" was a super rare badging for like, workgroup servers
the big rackmount units for the sun4m era were still VME systems: 4/670, 4/690, etc
they were workhorses for what we tasked them to.
not quibbling with your contribution, it's valuable. But if we're going to be more pedantic, a "server" is a piece of software, a single service running on a box and, in the realm of tcp/ip, listening to a port. I'm reading this on my X server.