52 or 53 model 99?

[chainsaw]

picked up a model 99 with '53 serial number but has 19D in the circle stamp.according to the chart it is supposed to be a single digit numer and the D indicates '52 manufacture.can someone enlighten me?

[Travis98146]

Possibly a transition year build? Started in late '52 and production completed in '53? Though I don't think a 1 year date difference would change anything.