I'm trying to configure CBQoS persist for a customer network so as to monitor CBQoS statistics but it the command somehow doesn't appear on the router. "snmp-server ifindex persist" is already configured.
router(config)#snmp mib persist ?
circuit Circuit MIB persistence
event event MIB persistence
expression expression MIB persistence
The router is loaded with this image - c2800nm-advipservicesk9-mz.124-23.bin which seemed to be suitable version according to this page
What did I leave out?
I could be mistaken, but isn't c2800nm-advipservicesk9-mz.124-23.bin IOS 12.4(23) "mainline"? The URL you're quoting is for 12.4(4)T, in which the "T" stands for "Technology". It's one of those confusing aspects of IOS naming convention, but those two are apparently two different "trains", with the "T" images packing more features but maybe also more bug-prone.
The cbqos keyword has been added to the "snmp mib persist cbqos" global command starting from 12.4(4)T, but most often not in the mainline code until a much later release.