I noticed there aren't alot of photos in the guide for this species. Are they uncommon, secretive or just generally overlooked? ...oh, and can you give me a brief lesson on yellowjacket / hornet / wasp nomenclature?

each play a role, They are not so common, especially in the South where they occur only in mountainous regions. For sure they are ratther secretive, e.g. never looking for human food like workers of more common species. And they are easily overlooked since easily mistaken for small Bald-faced Hormets, whose color pattern is very similar.
"Humeral" stripes are the white triangles in front of the thorax, near the "neck". Cleypeus (latin for "shield") is the roundish sclerite on the lower part of the face, just above the mandibles. I hope I have answered your questions.