When I was first told about this difference I concluded that it was yet another case of poor registration on a Walsall printed booklet.
On most of the booklet we have the window frames in the tower are doubled due to mis-registration, and the thickness of the caption bar, BOSTON MANOR ART DECO STATION, on the booklet stamp is thinner than on the sheet stamp.
However, Dominic has now sent scans of two booklet stamps which show not only that the vertical height of that blue bar is variable (as might be expected from mis-registration), but that the spur up towards the date 1934 is also different.
Although there is some mis-registration on the left-hand stamp (see the shadow on the Queen's head and the ghostly grey colour of the face value), the thinness of the bar below 1934 is much thinner on the left-hand stamp than on the right.
And if you look at the blue caption below the stamp, this also seems to be shorter on the right-hand stamp, although that may be a trick of the scanner: I've asked for that to be checked.
UPDATE 25 January: My thanks to John G for this larger picture of the lower right corner. This clearly shows that, while the amount of dark blue appearing in the spur is partly governed by the white space in the bluc background, the actual dimensions of the dark blue print are much greater in the right-hand stamp than in the left. There are definitely at least two versions. But why? There should be one image dropped into every position on the cylinder.
Is it time for Walsall to give up printing these multi-coloured booklets? One customer rejected multiple copies of the Queen's Diamond Jubilee booklet from other sources and asked if we had just one with the face value in white instead of with a cyan or magenta edge. In fact we have several, but it did seem that the 'good' ones were not as common as the blurred ones.
GERMANT ~ Germany ATM FDC - Germany 2017 ATM FDC, posted on January 3, 2017 from Bonn to Taipei with arrival postmarked on January 19, 2017.