The Amazing Sinking...Monument?

Canada Scott #247 has an interesting variation that one does not often see discussed but that is very easy to come across when multiples of the stamp are available for examination.  This stamp, part of a set of three issued for the Royal Visit (Scott #246-248) in 1939 were the first Canadian stamps produced with two separate engraved plates.  One plate was used for the color portions of the stamps and another for the black and white portions.

In the case of Scott #247, the black and white portion is the National War Memorial monument.  Because of the use of the two separate plates, the monument is not placed excatly the same in every printing.  As a result, stamps range from showing all the steps at the bottom of the monument to only one step.

In the examples below, the first stamp shows the full number of stairs.  The next stamp has only three stairs showing, the third stamp only two and the final stamp shows only one step.  When placed side by side, it appears the monument is sinking.

This being an inexpensive stamp to purchase, it's very easy for the collector to assemble a set showing all the different monument heights. Have you had any experience with this or other stamps with similar variations? I'd love to hear about it!

For additional information on the postal history associated with the Canadian Royal Visit of 1939, see this article by John Burnett of the British North America Philatelic Society:

Covers Commemorated the Royal Visit of 1939