BA11-C and BA11-E mounting boxes

For some actual content about classic computers (instead of flaming about various ideas for improving existing systems), I think I've worked out why the BA11-C and BA11-E mounting boxes have out of sequence variant codes. It's obvious the variants were not assigned in creation order (the /44 and /24 use the -A variant box), but the -C and -E (the earliest variants, it seems) apparently come from the fact that the first is used to hold the CPU and console (for the /20), and the latter is an Expansion box. And speaking of the -C/-E, somewhat to my surprise, I've discovered that their H720 Power Supply is actually a switching supply. Ironically, its manual gives a _far_ better explanation of the EI conversion concept than the later H742 one (which we discussed here at some length, after it confused me no end). Speak of BA11 variants, I've seen mention a BA11-B on Web sites, but only a single ref in a DEC manual (the DH11 Maint Man); does anyone have a pointer to a location where it's dicussed at more length? If so, thanks! Noel