Interesting. Of course, the oft quoted 21-25d usually means parallel or slightly positive vta. I don't think there is a rule: mostly a combo of urban legend and different specs/ manufacturer.
I'm not being helpful, but the problem usually lies not only in how the record was cut (about which one can only speculate, or generalise), but also on how the stylus was cut (as you note) & attached to the cantilever -- i.e. at what angle is the stylus expected to reach optimum tracking? It is a lovely example of hi-end imprecision: manufacturers raise the point and conveniently let it "float" without a solution...
I remember a V15 & Pickering 5k I had both "allowed" for negative vta. OTOH, IIRC, a VdH mc20 (OK it was mc) recommended slightly positive vta... "particularly for older records".
Other than the legends that parabolic was more tolerant of vta (hence negative) but shiabata allowed better info retrieval & longer life, I have never seen actual steadfast rule about this.
I'm not being helpful, but the problem usually lies not only in how the record was cut (about which one can only speculate, or generalise), but also on how the stylus was cut (as you note) & attached to the cantilever -- i.e. at what angle is the stylus expected to reach optimum tracking? It is a lovely example of hi-end imprecision: manufacturers raise the point and conveniently let it "float" without a solution...
I remember a V15 & Pickering 5k I had both "allowed" for negative vta. OTOH, IIRC, a VdH mc20 (OK it was mc) recommended slightly positive vta... "particularly for older records".
Other than the legends that parabolic was more tolerant of vta (hence negative) but shiabata allowed better info retrieval & longer life, I have never seen actual steadfast rule about this.