| There is little point in worrying whether a perf 10 thirty-cent single has a watermark. It has been
shown that the layout of the single-line watermarks sometimes allowed for an individual stamp to be missed,
while its neighbors were watermarked. Unless provenance can directly prove the stamp came from one of the known unwatermarked
panes, singles, even with absolutely no sign of watermark, can not be positively identified as having been printed on an
unwatermarked sheet and can not be certified. In particular, a used single has no chance of being certified since its provenance
will always remain uncertain. |