My single flat door Sport 19A definitely qualifies as a "Mouse" but as to the Sierra, that may not be so applicable.
The Sierra is the top of the line "Musketeer", and I think that might be why Beech kind of forgot the Musketeer name and came up with a high line name like Sierra. That was also the top of the line GMC pickup for quite awhile as well - then there was the High Sierra, and now the Denali.