……or is it?
A duplex was a hand stamp used to cancel postage stamps. The device had a steel die, generally circular that printed the location of the cancel and was usually identified by a letter and number.
The One Penny Lilac Postage Stamp was first issued on 12 July 1881. It was produced from Die No.1 and 495,984,000 were printed.
Between 13 December 1881 and 1901, Die No.2 was used to produce a slight design difference in the stamp and 33,600,000,000 were printed.
Die No.1. The stamp had 14 dots in each corner.
Die No.2. The stamp had 16 dots in each corner.