The Illinois Natural History Survey collection had one specimen that I noticed that looks consistent with Type B collected 10/30/1991 https://www.gbif.org/occurrence/3801314950, but it is further west than the current observations on iNaturalist.
Side view, Dorsal view, Angled view.
There are three pockets of observations on iNat for this group:
1) Chiapas (4. 3 females 1 male)
2) Oaxaca (30. 29 females 1 male)
3) Puebla (4. 3 females 1 male)
The males all show typical Thoracobombus long antennae, few yellow hairs intermixed on the face, black scutellum, and some yellow on T1 reminiscent of a classic pensylvanicus, full yellow on T2 & 3, none of the three show visible yellow below T3. One (Chiapas) shows few yellow hairs at the fringe of the scutellum and red/orange hairs on T5-7.
2 females in Chiapas resemble a classic pensylvanicus/sonorus except for totally black scutellum and T1 as described in the paper. 1 seemed to show a black scutellum but T1 wasn't clear, presumably black though.
The females in Oaxaca had some variance. For the scutellum: 21 had a black scutellum with no visible yellow hairs, 6 had some visible yellow, 2 unknown. For T1: 10 had T1 black with no visible yellow hairs, 12 had a thin line of yellow along the bottom, 7 unknown.
The females in Puebla show few yellow hairs around the fringe of the scutellum, and notable yellow along the bottom of T1. A female specimen from the Illinois Natural History Survey collection (see next post )collected west of Puebla, show faint yellow hairs around the fringe of the scutellum and a thin yellow line on the bottom of T1.
Discussion
The visible yellow in the scutellum in all of these was very faint and around the back edge, it also in some cases appeared to be only visible from the side and not from the top down, so it might be more prevalent than appears. The visible yellow on T1 for all of these is very thin much more subtle than what is seen on a classic pensylvanicus. As such it also may be more prevalent if photos are seen from different angles.
As a side note, please be aware that these numbers are from "eyeballing" photos of various quality. Another reviewer may come up with different numbers. Also there is not a guarantee that all of these are indeed Type B.
