when combined with actual eye injuries
Doesn’t take much for memetics to kick in
That alone is enough to explain our observations (the trope).
So, to summarize your point, if this happened but not very often, it wouldn’t leave any evidence. We have no evidence, therefore it must have happened, just not very often.
Probably, there may be evidence if you cross referenced a bunch of old journals, possibly medical logs, and maybe familial oral traditions. But yeah without going through largely inane and scattered documents it’s probably one of those self perpetuating memetic things that pops up on occasion because for a short period of time an uptick in sailors with eye patches happened and it got stuck culturally.
The best you could probably do to actually disprove such a thing would be to find where the source was, which would in all likelihood come down to a certain model of ship or a specific cultural tradition. Hell given how commonly shit goes back to Odin it could be a lost form of worship that got wrapped up in with sailor folklore after the viking age.
