I also feel that much of the history of this icon may be off. The persons who bequeathed it to them were Jewish and had simply bought it somewhere. The art market was inundated with icons from Russia from after the Revolution, and they were often passed off to buyers by clueless art dealers for something they were not. Neither dealers nor buyers knew much about Russian iconography decades ago.
The best way for the parish to find out would be to take it to a museum like the Metropolitan to have the experts date both the icon and the icon cover for them.
On the other hand, it is Our Lady's miraculous presence that really matters.