6R5.1 Another 5 on 6 at Pos. A10?

6R5.1 Yet another '5 on 6'?

Plate Position - Plate A, Position 10.

ERU =

LRU =

Multiples: From the Upper Right of a mint block of at least 4 from the WLS collection.

Confidence in identification: 100%

Notes: This stamp has bothered me for a while. Now that multiple copies have been found, I have a theory which should at least encourage discussion.
This link is to an image of the full stamp.
This link attempts to explain my theory.