If not even Mathematics can be complete and consistent, I am always very cautious with any 'carved in stone'zation of languages.
1. Is this word really out of the dictionaries?
Any inquisitor should be prudent when claiming such thing since some words are in some dictionaries but not in others.
2. So words not in the dictionary doen't exist?
The language is a living thing...but lets answer this with Prof. Moreno's quote in his article about the dictionaries Aurélio and Houaiss:
Para aqueles que pensam que só as palavras que estão dicionarizadas têm direito a existir, informo que nenhum dos dois registra agroexportador, antimotim, antiestatizante, autolimpante, bivolt, bloqueto, civilizatória, degravação, drogadito, drogadição, intensivista, mecatrônica, rinsagem.
For those who think only words in the dictionary have the right to exist, I tell you that none of them contains agroexportador, antimotim, antiestatizante, autolimpante, bivolt, bloqueto, civilizatória, degravação, drogadito, drogadição, intensivista, mecatrônica, rinsagem.
3. Yay, I found the word! So...How do I know if it is easily answered by the entry?
Assuming that dictionaries register all possible uses of that word [or at least all gramatical classes], one might say ''but it's written right there that
detrás is an adverb never an adjective''; and some might say that this is not trivial, quite the contrary.
There is no axioms from where we can prove/deduce that something is 'easy' in Portuguese.
That being said, to avoid
should I write 'vossê' or 'você' questions, the only thing to do is to flag it as off-topic/stupid/gimmeabreak or whatever you want and wait for people to agree with you. Maybe even open a Meta post to convince them.
Because in the end what is the truth other than something that most people agree with?