1904, 8c on 50c Bister Brown,
"Canal Zone" Inverted (14b). Barely hinged, rich color, almost perfect
centering, Extremely Fine, a superb example of this variety, only 200 were
printed, see lot 532 for description of its discovery, with copy of 1969
A.P.S. certificate for block of eight, this being the top right stamp (Image) 
1904, 8c on 50c Bister Brown,
"Canal Zone" Inverted, Right "Panama" 5mm Below Bar (14b var). H.r.,
deep rich color, almost perfectly centered, Extremely Fine, scarce variety,
only four were printed, Scott Retail as normal variety
(Image)
1904, 8c on 50c Bister Brown,
"Canal Zone" Inverted (14b). Mint N.H. block of four, crisp impression,
remarkably freshEXTREMELY FINE. A VERY RARE MULTIPLE OF THE 1904 8-CENT SURCHARGE WITH "CANAL ZONE" INVERTED.
According to Canal Zone Stamps, the two error panes of 100 were sold in 1908 by their original owner, who claimed to have purchased them at the Administration Building in Ancon.
With 1969 A.P.S. certificate for block of eight, this being the center block, Scott Retail as hinged singles (Image)
1904, 8c on 50c Bister Brown,
"Canal Zone" Inverted (14b). Block of four, barely tropicalized
original gum, bottom stamps Mint N.H., top right stamp spaced "A L"
variety, deep rich colorVERY FINE AND CHOICE. ONLY TWO WERE PRINTED WITH THE SPACED "A L" OVERPRINT VARIETY. A GREAT RARITY.
Only 200 inverted overprints were printed in total. Of these, only two (one per pane) were printed with the wide "A L" spacing variety.
Small green backstamps. With 1972 A.P.S. certificate, Scott Retail as four inverted overprint singles with no premium for the variety (Image)
1904, 8c on 50c Bister Brown,
"Panama" Ovpt. in Rose Brown, "Canal" in Antique Type (14d). Bottom
stamp in vertical pair with normal, Positions 16/26, lightly
hingedEXTREMELY FINE. ONLY AN ESTIMATED TEN COPIES WERE PRINTED, OF WHICH ONLY FOUR ARE RECORDED. A GREAT RARITY.
Ex Plass. With 1993 P.F. certificate. (Image)
1904. 8c on 50c Bister Brown,
"Panama" Ovpt. in Rose Brown, "Zone" in Antique Type (14e). Top right
stamp in block of four, Positions 47-48/57-58, slightly tropicalized
original gum, "Panama" shifted significantly to right, deep rich
colorsVERY FINE AND CHOICE. AN EXCEEDINGLY RARE BLOCK OF THE ROSE BROWN OVERPRINT CONTAINING ONE STAMP WITH "ZONE" IN ANTIQUE TYPE.
According to Canal Zone Stamps, only an estimated ten copies of this variety were issued. Of these, perhaps five are known, including one in a pair with normal (ex Plass), one in right margin block of six with imprint (illustrated in Canal Zone Stamps) and one in block of four with small fault in bottom margin (ex Tows).
Small green backstamps. With 1969 A.P.S. certificate. (Image)
1904, 8c on 50c Bister Brown,
"Panama" Ovpt. in Rose Brown, "8cts" Double (14f). Unused (no gum),
deep rich colors, fresh and Fine, scarce, according to Canal Zone
Stamps, only 30 were printed (25 from the lower right quadrant of one
pane and five from the top row or a quadrant of another)
(Image)
1904, 8c on 50c Bister Brown,
"Panama" Ovpt. in Rose Brown, "8" Omitted (14g). Left margin block of
four, top left stamp (Position 1) the error, "Panama" overprints shifted to
left so that "Panama" reads up and down close to one another and is
completely missing at left side of right stamps, small h.r.FINE AND RARE. THIS IS THE LISTING EXAMPLE OF THE "8" OMITTED ERROR. A TOTAL OF SIX WERE PRINTED.
According to Canal Zone Stamps, all other examples of this variety were caused by shifted overprints where "cts" is split horizontally on the stamp. To our knowledge, this is the only example with the "8" missing due to either the "8" falling out of the typeset form or from foreign matter blocking the impression.
Ex Plass. Illustrated in Canal Zone Stamps on p. 53. With 1967 P.F. certificate. Scott Retail as error and three normal stamps with no premium for shifted overprint variety. (Image)