Thirty-two different type/positions

types/positions     absolute watermark
according to BvdB   positions   a - h

   IVb-R-left       [c]?
        -right      [a]
        -up         [b]
        -down       [d]

   IVd-R-left       [c]?
        -right       a
        -up          b
        -down        d

  'IVb-R-left        g
        -right       e
        -up          h
        -down        f

  'IVd-R-left        g
        -right       e
        -up          h
        -down        f

   IVb-L-left         e
        -right       [g]
        -up          [h]
        -down         f

   IVd-L-left         e
        -right       [g]
        -up          [h]
        -down         f

  'IVb-L-left         a
        -right       [c]
        -up          [b]
        -down         d

  'IVd-L-left        [a]
        -right       [c]
        -up          [b]
        -down        [d]

All in [ ] not yet found. Position b. is only known in the 1956 8th Independence Day stamps. Position c. sofar only in the 1958 10 ship stamp. I Dont' know whether IVb-R-left or IVd-R-left. The latter seems more likely since no other IVb-R has been found.