A Christmas Seal Error is a mistake in the printing or perforation, made by accident. This collection of Christmas Seal errors is not complete and includes 1) missing colors, 2) inverted colors, and 3) pairs with missing rows of perforations, where vertical or horizontal row(s) were omitted (creating HPIB, VPIB, HPIV and VPIH)
HPIB- horizontal pair imperf between, may come from a sheet missing a single vertical row (or every other vertical rows) of perfs.
HPIV - horizontal pair imperf vertically typically comes from a sheet missing all vertical perfs, and is imperf on the right and left side.
Same for VPIB - vertical pair imperforate between, and VPIH - vertical pair imperforate horizontally
HP-IB, HP-IV, VP-IB, and VP-IH - This is an old seal collecting designation for a gutter pair. The "-" indicates that the seals came from 2 different panes. These are not errors, and were excluded. 1908 type 1 exists as such a gutter pair (from an uncut booklet sheet) and is often considered an error, but it is not.
Missing color errors can be confused with a stage of a progressive color proof (pcp), however they are either a different perforation, or a different combination of colors.
Worn plate varieties such as 1936 missing candle flame, or 1941 no footprints in the snow, though listed in Green's Catalog as errors, really are not. Also, printer's waste, which can look a lot like errors, were also excluded from this image collection. Seals with a doubling (or tripling) of a color, where the subsequent print is lighter, did not actually run thru the press twice, and are not included here. Grossly misperforated sheets, where perforated and imperforate seals exist side by side, though errors, were also excluded.