> Cioè, sarebbe erroneo impiegare questo dubitativo per confermare qualcosa? non equivale a?:ti eri mangiato il dessert prima di aver finito tutti gli spaghetti persino innanzi ai tuoi capi?
> Perché? Quali sono le condizioni che impone?
> Forse ha un valore di congettura ovvero supposizione?
Sorry, but I'm still unable to understand both the meaning and the purpose of your example sentence, unless you are wondering whether this kind of subjunctive could be used to ask for confirmation (which in Italian would translate to "chiedere conferma di qualcosa").
If this is the case, the answer is sort of yes, but you have to take into account that this kind of subjunctive always expresses a hypothesis (both when the sentence is introduced by 'che' and when it isn't), so that an interlocutor can give a confirmation, but only referring to the hypothesis, not to a fact. Maybe your sentence complies with all I wrote, but I can't confirm it, because I'm not sure about its meaning; I suggest that you try to write a much simpler one, containing only what's necessary to analize the conjugation you're interested in.
Anyway, here comes an example of confirmation:
person A) – Come avrà fatto a sfuggirci?!
person B) – Che avesse subodorato qualcosa quando abbiamo fatto irruzione in quel magazzino, prima che noi decidessimo la retata?
person C, confirming) – È proprio così: mi hanno appena fatto sapere che qualcuno gliene aveva parlato.
Please, remember the note of caution contained in my previous message regarding the choice of the trapassato tense of subjunctive in the second sentence.