It’s not really a gem per se (and I know you’re being sarcastic here, which is OK with me), it’s just based on my personal experience, and also common sense in the observation that most HA mfgs don’t bother with amplifying about 8 KHz anyway. I’ve never seen any HCP do any audiogram above 8 KHz either.
My personal experience is that I’ve spent money to go for 105 dB receivers with custom molds for my hearing loss (severe to profound at around 2 KHz and up), with the hope that these receivers would let me hear “something” at the 3, 4, 6 and 8 KHz regions because they’re supposed to be able to handle that kind of loss. Unfortunately, even with 105 dB receivers in custom molds, I could hear none of those pure tones in an in-situ audiometry test with my OPN 1. I could definitely hear the buzzing noise of the receivers being driven so hard that they probably vibrated violently and created that buzzing sound every time I push the pure tone test button (probably at a vibrating frequency that happens to be within my lower frequency audible zone), but I was not able to hear any of those 3 - 8 KHz pure test tones at all. Nothing, cricket. My personal conclusion is that I have cochlear dead zone in that space and no amount of amplification can vibrate any of the auditory nerves which I no longer even have in those cochlear dead zones in the first place.
I understand that there are MANY different reasons why HA mfgs choose not to go above 8 KHz, not just because of the reason I cited where I think that hearing beyond 8 KHz cannot be restored that easily (like I suggest). There’s also focus on only speech consideration, there’s also the economic consideration of a lower sampling rate, there’s also sensitivity to feedback consideration, there’s probably even safety consideration for amplifying sounds above 115 dB SPL (sound pressure level), etc. But since you asked a valid question here, I tried to Google the question and found this link Humans can hear frequencies up to 20 kHz. Why don't hearing aids provide sound at frequencies above 10 kHz.
In this link for this question, many HCPs chimed in and offered their opinions on this question. I found 1 HCP’s opinion (which I copied and pasted below) that resonates most closely to what I suggested about people with significant high frequency hearing loss (2 KHz to 8 KHz) not having any usable hearing left above the 8 KHz range. It’s specifically in his last paragraph cited below.
