What the...???

[DonVoigt]

Originally Posted by DavidJayUden

Can we safely assume that late in the war it was probably a matter of whatever was available?
dju

Sort of,
a decision was taken to move to all "simple" sights; but old parts continued to be used up.

Rarely a matching fine tune rear sight will show up on a 1918- I think two have been reported.

In 1917 there is a general trend from both fine tuned to both "fixed" as production progressed, but fine tune sights show up till the end of 1917.

No hard or fast rule!