Parthian Shot vs. Parting shot

[Laudenum]

Wiki has this:

The term “parting shot,” used similarly, may be a folk etymology of “Parthian shot,” meaning the term was corrupted through common parlance, but there is little firm evidence to support this claim

I was just reading Sherlock Holmes when I hit on this phrase (Parthian shot), and I had to look it up. It seems incredibly similar to “parting shot” in meaning and sound, and I was wondering if anyone here could give me a firmer answer than wiki.

Which came first?
Did one beget the other?

[Earl_Snake-Hips_Tucker]

This attests it from 1590, though it doesn’t give a source.

ETA: OED concurs.

[Quartz]

I suppose the difference is that the Parthians charged into range, shot, then charged out of range, then repeated the exercise, whereas with a parting shot, you don’t get a second go.