There are definitely two versions, one that keeps the pump running after you release the trigger and one that doesn't, the front panel was a lighter grey on one of them, don't know which was the older one, the motors failed open circuit in both after many years of use.
Edit: for the MBT201 it describes this in the manual, only versions with an A after the model number, run the pump for a minimum of 1.2 seconds, this is branded as "Auto Snap-Vac".
David