I dont know the exact date but the midget jars were ended fairly early.
One of the jar people can probably tell you.
The lid size would be the reason. They just went to the pints with the normal lids. Then people could use the regular lids and the opening of the jar was bigger. Probably made it easier to make the molds too.
Another thought along those same lines... I've never seen a "real" midget with a smooth lip, so that would make their demise some time before 1900. Here's a not-so-good photo of our set of 4 Mason's Patents. The half pint is unembossed.