Hmm. MDOT's updated GIS is not showing the route numbers (or I just can't figure out how to make them visible), but that segment has the same control number as the 94BS east of M-96. That, along with the signs, makes me want to include it.
However, the same GIS shows West Main St east of US 131 being part of M-43 (well, the same control number as M-43 west of 131). GMSV from Sept 2019 also shows M-43 heading west and east at that interchange.
M-343 is signed in GMSV (also Sept 2019).
This needs more investigation.