git describe --tags b9a3c08 says v1.1-14-gb9a3c08, so I think you want

DISTVERSIONPREFIX=v
DISTVERSION= 1.1-14
DISTVERSIONSUFFIX= -gb9a3c08

and you can remove GH_TAGNAME below.

Do you need to loop here? It's only installing one file.

NO_ARCH= yes as well

To use PORTDOCS, you need to add OPTIONS_DEFINE=DOCS.

Why += ?

dch, you can verify the += isn't necessary with make -VPLIST_FILES.

no good reason - thanks Mat!

Nit-picking: It looks like a tab is missing here. Do you want to add one?

missing tab?

done - also one for DISTVERSIONPREFIX= too. Is there a rule along the lines of: use vim tabstop=8) and always 1 space even if it looks weird sometimes?

I see there's tabstop=4 for *.Mk files listed in the handbook but it doesn't seem to be consistent in the ports I've read so far.

The rule is put at least one tab after the =, and tabs are 8 spaces wide.
For the "looks wierd", YMMV.