Very rare error in the date - with 1009 instead of 1609.
The effect of unfinished digit "6" on the stamp (lack of tail distinct, not due to deficiency). An article on this unusual form of date preparation on Vilnius pennies available at SpodStempla.pl.
The penny, whose rarity Kopicki estimated at grade R8, and Ivanauskas noted an error of 1000 (rather than 1009).