I am working in a "normal" sheet-fed offset printing company with the usual portfolio: Posters, postcards, information- and self-presentation brochures, books (including art catalogs), and sometimes even packaging with subsequent individual finishing ...
I think that in order to obtain usable answers for you, you should know whether it is a matter of high-end control of high-quality periodically recurring packaging such as globally marketed cosmetics or "only" the "sporadic" use of special colors in existing CI's s or more or less experimentally creative use in graphic design or in duplexes or even triplexes ...
We do not work according to ISO20654.
In any case, we do not bother to record the spectral value of a 50% tone for estimated over 50 different spotcolors used per year and to recalibrate it via an extra curve in the RIP.
For "tricky" jobs, we sell a real print as an advance proof on edition paper in advance. Simply the cyan correction curve is stored for the exposure for FOGRA39 and 47 jobs. (because a color is mostly more near by Cyan or Magenta than black and black in FOGRA39 and 47 expect some more increase than C+M...)
Exceptions confirm the rule, there may well be a need to proceed differently elsewhere... but I think it makes sense to realize that spot colors have their original justification in the reproducible solid tone beyond color stability, color mixing and register problems to print, which can also be outside the usual CMYK color space.
Of course, tonal values can also be mapped / generated from it, or creative elements such as gradients can be used, but just because it is technically possible does not have to legitimize an enforceable "misuse" of the original concept ...: For everyday industrial production, it is already a challenge enough to use spotcolors to get the same full shade on different, even the same substrates ...
As I said, in the packaging industry there may be a need for more dedicated control here, but definitely not in this company, although i would say it is a quality-shop.
