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Inverted Centre Stamp
Saudi Arabia (HEJAZ)
Sellinger 1, Scott L50a, SG 58a variety, MNH. 1924, 10p Arms of the Sheriff of Mecca with inverted centre.
According to Sellinger, between100 - 200 exist.

Some stamps used to require a second or third manual feed through the printing press after changing the ink in the press. When the sheet was accidentally fed upside-down for its second passage through the press, an inverted centre would result.