What is a model variation?
What could be understand as a variation? Is the box colour a variation to cover with a note in Notes or enough to make a new model.
Some Philips manuals show a lot of letters after the model number and each pair mean a different colour.
I understand it when metallic or wood, export model, tablemodel and then rack or furniture or radiogramola, but would like to know if anything is enough, by example the same model make for 25c/s and 50c/s mains, or 110V and later 127V adopting new standard mains. Because then, if a model maker stated eaf41 and eaf42 for same tube, must done a model for eaf41 and another for eaf42? Nope, ussually listed as EAF41 or EAF42.
As long as the names and numbers of two almost (!) similar models are different we use them as separate models.
In particular in the USA often separate colors got individual suffixes which necessitates separate records.
If several colors are available but not noted marked in the name, then the colors shall be mentioned in remarks of the common model. There must not be any other difference but the color !
If two almost similar models have identical name and number, but differ in some other respect: e.g. other tubes not interchangeable, other number of speakers, different scale (but from same country), different shape (e.g. slant panel vs.vertical panel), then a distinctive characteristic shall come into the variant fields of both models(!).
There is never a single variant.
Now to Your questions, Miguel:
since EAF41 and EAF42 are not generally interchangable (only if socket pins 1 and 7 are connected) I would see two variants. The "or" between two tubes means fully replacable by... hence listing EAF41 or EAF42 is not correct if not a.m. provision (pin 1-7) is verified and noted in remarks.
The 25 Hz mains case: certain manufacturers mark it e.g. by suffix . Such models are easily distinguishable if a label is found. In all other cases I would prefer to mention 25 Hz and 220 Volt variants in the remarks. From a front shot there is no hint which chassis, mains transformer and filter caps are behind. So even marked variants could be treated together. We must always consider the traceabilityof our models. It really depends, and I fear we cannot establish 100% strict rules. Common sense is indispensable.
I am not aware of a variant of the same model to adopt new mains standards e.g. from 110 to 117 (127?) Volts. That may be an academic problem, not a practical one.