If the links to download firmware are dead, your only hope is to get your hands on a ProLiant Support Pack that does support your server hardware.
I don't have my HPe login near, but check there for older version of it;
HP Service Pack for ProLiant
As stated in comments, please advise your customer.
You're pretty much right: with KB.jj.ii.bbbb, KB indicates the switch series, jj the major release (releases may differ considerably, web interface changes, command changes), ii the minor release (generally compatible but features may be added), and bbbb is the build/patch level, removing bugs mostly.
Generally, you'd want the latest/greatest. But if you can'...