RD26 Perf 10 With O/P Lines 9mm Apart

I have a Documentary stamp in Scott R22 format, perf 10, color medium red.
Scott lists seven R22 red (actually carmine rose) issues:
R231 perf 11
RC3 perf 12
RG4 perf 11
RJA11, 28A and 36, all perf 11 with NARCOTIC o/p
and mine,
RD26 perf 10 with block sans serif STOCK TRANSFER o/p spaced 8mm apart.

Only problem is that mine has 9mm space between STOCK and TRANSFER.
Is this just nit-picky or is it a known error or oddity? Thank you!

Is it possible to show a picture?


Peter

Here is the RD26 stamp mentioned in original post

With that blown-up pic, I note that STOCK TRANSFER does have serifs after all.

Measuring the blown-up picture gives a spread of 8.5mm, not 9mm, between STOCK and TRANSFER. Seems like that might be within the allowable tolerance. I'm leaning toward "nit-picky".