James J. Matejka., M.d. Czech Airmail Discovery.

Today shareing a Christmas gift from years back {1969}

I received from the Doctor who was a member of our local stamp club . He was the one who discovered this variety .It is the "no hill" on the left variety of Czechoslovakia 1930 airmail stamp ,scott C-13. The Scott Classic mentions this variety .
Dr. Matejka and Joseph Jiranek both did extensive studying and research on all the perforations,design size and varities of these airmail stamps .

Notice below on the far left side the hill above the 3 is missing.

Interesting. The Czech Pofis specialized catalog (2005) shows this as Type I, based on the "3" sloping to the right. It does not mention the missing hill. Types II and III both have the "3" in a normal upright position. II and III appear to differ in the density of the cross-hatching directly above the "3 Kc" (the Google translation is not clear).

The number 3 also looks re-engraved or "re-entered".