Why not produce the NVIs in sheets of 25 instead of making extra work?

Most people who collect Machin definitives will know that they are printed in sheets containing either 25 or 50 stamps.  The valued stamps and Special Delivery are in sheets of 25, the other NVIs are in guttered sheets of 50.

In the Wilding era lower value stamps were printed in sheets of 240 to make accounting easy: 240 x 1d = £1, 240 x 1/- (12d) = £12.  In the decimal period sheets originally contained 200 stamps for similar reasons.  These sheets had to be folded or torn apart in order to fit into counter books at Post Offices.

The introduction of the self-adhesive sheets of 'security' Machins saw a reduction in size to 25 for the high values values and 50 (with a gutter) for the NVIs, while the other (gummed) valued stamps continued in sheets of 200.  Now all new counter sheets are self-adhesive and all valued stamps are in 25s.   The marginal markings include cylinder numbers and printing dates (for Royal Mail, or just for us?), and a bar-code and short title for Post Office.  This bar code is not used for point of sale scanning, but only for warehouse stock control, we understand.


This year the sheets of 50 started appearing with the barcode and short title printed twice on the back of the sheet in black, as well as on the front in black (barcode) and the colour of the stamp (short title).  The reason for this is that the sheets are now supplied from the printers pre-folded (as we found with the Christmas sheets), leaving the barcode hidden!

 

The 1st class, and 1st & 2nd Large were printed on 18/04/19 with an additional row of rouletting in the central gutter.  The 1st Large was later found from the same printing with the new reverse printing but without the extra rouletting!  My thanks to RP for the pictures below, which I should have shown earlier: the arrival of the new September reprints (above) is what prompted me.  Click on the images to see them much larger.

 

UPDATE:  In the comments Anonymous wrote:

Anonymous 29 October 2019 at 13:30

From the image, it’s hard to tell if the panes are separated by a gutter or if the panes are unseparated panes of twenty five stamps without a gutter (which they appear to be). The gutter (the piece of backing paper) between the panes was the size of a stamp.

No, you are incorrect.  The gutter between the panes is smaller than the height of the stamp, it is the same size as the top and bottom margins combined.  This is why sheets of 50 are twice the size of sheets of 25, which are guillotined in what would be the gutter.  See picture below for a scan of the M17L 1st Large

 

  

It is, of course, up to collectors just how many of these they collect and display in their collections.  As the two sides of the reel are probably printed in one operation it is unlikely that there will be any displacement of the reverse printing as there was decades ago with the misplaced phosphor cylinder numbers, but it is probably worth looking whenever you get an opportunity, to see just what else is happening in the weird and wonderful world of Machins!

But why did Royal Mail or Post Office persist in sheets of 50, involving the additional printing.  Why not just make them all sheets of 25?

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