Proposed new variant subtag: pre1917

[Caoimhin O Donnaile]

>> Or indeed 1918ortho, which would disambiguate which 1918 change we are
>> referring to. I am not insistent on having a name in the tag.
>
> Remember that variant subtags may not be longer than eight characters;
> also, if they start with a digit, they must be followed by precisely
> three characters for a total length of four characters (and if they
> start with a letter, they must be followed by at least four characters
> for a minimum length of five characters).

"orth1918" ?