The mention "This term is for CLASSIFICATION ONLY; DO NOT USE term in indexing. Use a more precise narrower term." should only apply to the root (highest) descriptor in the hierarchy. The intermediate headings should be "Whenever possible, use a more precise narrower term."
When using a thesaurus to index data, one chooses the most precise descriptor available, but if that term is not availabe (perhaps not yet created), one chooses the higher descriptor. For example, if you know a value was created by analysis but cannot find or do not know the precise method, then MIR003 is not satisfying, as that code is used when nothing is known, not even whether it was calculated/ imputed.
Also, when aggregating initial values created by different analytical methods, one can always choose a more general method to describe the aggregated value (e.g. HPLC + GC = chromotography). But sometimes "Analytical method" is the correct higher term because the methods belong to different "families" (e.g. electrode + AAS) .
It is impossible to abide by the CLASSIFICATION ONLY rule in the Method Indicator thesaurus as it stands now.