How do you deal with discrepancy in informality between dictionaries? [closed]

Solution 1:

Language is vague and dictionaries aren't perfect themselves (that is to say that the world is variable but also the record of the world is variable).

Dictionaries are references and not necessarily fully defining. What they specify is mostly to be not wrong. Not saying that a word is informal is not wrong, (also the editing decision of a particular dictionary may be to use attributes like informal only in extremes).

The way I deal with multiple definitions that differ for terms that I have no idea about is to consider such attributes as possibles. If all the definitions have the same attribute (say informal) the word is most likely informal. If one of many misses the attribute then maybe it is a mistake or maybe it is not extremely informal. If only one out of many has the attribute, maybe it is a mistake or maybe it is slightly informal. If none have the attribute, it probably isn't informal (but maybe it is slightly informal.

You're never entirely sure about anything ever, but you can only see the data that you have. If there is a discrepancy look at more data/sources/dictionaries.