More about 1919 Armenia "k 60 k" overprints

Back in December, I blogged about the first stamp of independent Armenia. Now I illustrate the state of my stock - see below.
From a stockbook now containing over 250 "k 60 k" stamps I constructed this matrix:

ACROSS:

"k.60.k" in black on imperf, the same, but missing in violet; in black on perf, in violet on perf; "k 6 0 k" (wide setting) in black on imperf; "k 60 k" (narrow setting) in black on imperf

DOWN:
Additions to the basic stamps:
Framed Z in black
Framed Z in violet
Unframed Z (small) in black
Unframed Z (small) in violet
Unframed Z (large) in black
Unframed Z (large) in violet

What strikes me is how many gaps there are in the matrix: all of column 2 is empty. There is only one stamps in Row 3, and this is a "Serebrakian Special" with his small boxed handstamp on the back - Serebrakian generally reserved this handstamp for stamps which he had in only limited quantities, originally made for him as Counter Surcharges