significance of hyphens

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In the 1911 $1 notes and the 1914 $2 notes, earlier varieties did not have a hyphen between the series letter and the sheet number while later varieties did.  I suspect there is a reason that the hyphen was considered neccessary.  Does anyone know the reason?

Hyphens as such have no meaning. If we have a part number that is A-123456, accounting people have read that as A123456.
On a note it is read as nothing of importance, or nothing at all. There is and was no reason or meaning for the hyphen other than a space filler.

It is not used in place of another digit or letter, and sequentially, fills the roll of nothing at all.

Why did they use them in certain bank notes, and then drop their use? I don't know beyond what is stated above.

Rick