The issue is that your standard is borderline setting up an impossible strawman, and when we actually do textual (and/or biblical) analysis and historical science, we never really have a "this is THE version of Q" nor do we have a "this is the FINAL/REAL version of the book" or "this is the final/absolute version of the hypothesis".

The idea that there is "one authoritative version and it was the version that was copied into this one authoritative derivative and we found the derivative so now we have to find that exact original or else its all bumpkin" simply isn't the way 2000 year old books or texts were written, copied or used. You will never find it because that's not what happened.

But we can lay out the texts side by side, arrange the narratives and see how they differ chronologiaclly from book to book, notice where particular linguistic quirks take place, notice where words are copied word for word in a particular order, where embellishments or insertions or changes are made, then just like taking several witness accounts, we build up a probablistic version of events that happened.

So there isn't "one Q", just as there isn't one authoritative version of mark, luke, john, mathew, etc. But there's patterns in the texts which strongly suggest that there was some kind of shared knowledge and a common source in the authors of the later gospels. We hypothesised that this common source seemed to be shared amongst the other gospels was a "sayings gospel", because the common ground that seemed to be repeated in the other books were primarily sayings and the other bits seemed to come from mark, which at the time met the problem that people didn't accept that such a book or source would actually exist because we'd never seen one before.

Then, after this hypothesis was formed and that objection raised, with the discovery of the nag hammadi library and the gospel of thomas, we found an actual historical sayings gospel. A confirmation that this type of literature did exist and was written in early christian communities. It was not Q, but it confirmed the hypothesised genre and existance of early christian literature.

If you're waiting for the discovery of two literal peices of text, whereby the carbon copy of the first is deduced from the discovery of multiple other historical books to the letter that followed, well then you're setting up an impossible standard. Even literal transcription probably wouldn't meet that standard.