Nah, thats misleading. All devices by internet law (RFC1213) should answer sysDescr and SysObjectID and id say 99.100% of devices do and we of course have that public MIB2 already loaded. As you mention, its when you want very specific private information you would want to load the companies mib.
Ive explained in classes like this and (for the general audience). Suggy Switch company and Dougs Router company both have cpu's, interfaces, names ect ect. So we answer the same public MIB-2 question (OID) that we both will answer the equally by whoever asks.
Now Dougs routers also make coffee. So I would publish a private MIB with a questions (OIDs) you can ask about how the coffee maker works and is setup, items that Suggys Switches wouldnt know a thing about. This as you mentioned this is where you would load a private mib so you can extend/create your pattern to get those additional details in exploration. But classification, no private mibs needed, so yes the KB is misleading.
Now there was an occasion that we found that a manufacturer didn't answer the snmp SysOID but did through their private MIB, so a little tweak here and there and we got it returned so we could use it in the classification process.
Remember the SNMP sysOID list in your instance is also used to support setting manufacture and model so they can be really handy. But dont get me started on some lazy folks in the printer world who dont make their responses actually unique, but a story for a different time. Or look at the Printer classifier and see the 'triggers probe' section where we built a probe to combat those lazy jerks 🙂 🙂 Fairly it could be done in a pattern now, but it gives you a good reference on the flexibility you have in using the classification value that are set from the very beginning.
