Am I really?? You're the one claiming analog audio has fundamental recordings way past 20kHz (now claiming up to 120kHz). Even though none of us simple Head-Fi members can't measure anything of the sort, you're saying we're all crazy. What I think really telling: the audio source of something that might be over 20kHz is one reel to reel, and then when we get into a record "well I think instruments can get into that much more higher frequencies"
Well, if if none of the simple Head-Fi members can't measure anything of the sort, it does not mean it does not exist.
By sticking with RBCD, you also never will.
The same by reading the analog lathe manuals by their manufacturers - the best contraceptive ever is still an aspirine between the knees, however the amount of joy attainable in this fashion is somewhat limited !
None of the really good sounding records have ever been mastered on stock mastering lathes.
Situation today is even worse, as cutting heads are supported only by some very rare usually ex-employees of cutting head manufacturers - with only VERY few new/young guys willing and/or capable of carrying the torch further.
That means that cutting levels/frequency response extension beyond 20 kHz ( which requires very high power - reaching in total 900 watts for the peak high frequency content - the reason why helium cooled cutter heads exist )- is today FAR more conservative than back in the day, where burning a cutter head meant "only" some 10k$ and few days waiting for the delivery of the replacement.
Today, it means a LOOONG wait for the repair - half a year if not more, before any of the remaining people that can repair a burnt cutter head can repair yours - meaning you are out of bussiness for that long ! Not to mention the $$$$$.
No prize for guessing why today's requirements for preparing the master for analog record are more restrictive than ever before - and why cutting today is way below what cutter heads can actually deliver under optimum conditions.
Further limitation lies in the thickness of the mastering blank acetates. Back in the day, when Pyral has been located in Asnieres ( Paris suburb ) in France, the thickness of the lacquer ( which limits the maximum vertical excursion of the cutting stylus ) has been at least 70 micrometers - today's Pyral in USA only produces 60 micrometer thickness lacquers.
This fact made mastering studios limit the mastering for analog record even further - this time in the bass.
Vinyl records contain - besides the actual musical content - also LOTS of mastering "oopsie-daisies" - like artefacts/drones with the very precisely defined frequencies, starting at around 15 kHz - and stretching al the way just a hair below 70 kHz. They are actually a very good forensic tool - preserving for the posterity all engraved in their grooves - be it good or bad.
This of course requires both analog and digital equipment that can do the extended bandwidth full justice.
The above also explains why vintage pressings can and do usually sound better than their current re-releases - even in those rare cases when the entire recording chain has been kept strictly analog, without the vast majority of the lathes being fed from a digital file, usually required for the cutting computer to squeeze the maximum playing time without crisscrossing the actual grooves.
Pure analog cutting lathes available today worldwide are counted - at best - on the fingers of both hands. And even they can't replicate the vintage quality, due to the lack of thicker acetate blanks.