BruceRMcF said

brown.connor4 said
The question is, when?
If Mark was written circa 70 AD, and 1 Corinthians circa 55 AD, that is almost twenty years.  Did the first copy of 1 Corinthians sit in some home in Corinth gathering dust for twenty years, still remaining unknown to the Christian communities in Ephesus or Thessalonica or Rome?  Or is it more likely that within the these twenty or so years the letters of Paul were deemed authoritative and worthy of disseminating? …  

These are two extreme ends of a spectrum of possibilities, not two distinct alternatives, either one true or the other.
If your argument rests on the extreme ends being the only alternatives considered and all of the intermediate possibilities being treated as impossibilities, this would be the logical fallacy of false dichotomy, sometimes know as “the excluded middle”.
First, we don’t have evidence regarding how close the version of 1 Corinthians that we have is to any letter or letters written by Paul to an early community in Corinth. Assuming that the autograph is “reasonably close” to the canonical epistles is every bit as much of a speculative assumption as assuming that two original collections of epistles were faithfully copied into Marcion’s New Testament, and that proto-orthodox believers dramatically elaborated upon them in the middle of the 2nd century to create scriptures with authority that would be more resistant to Marcionite views, or that what we have received as two long letters to Corinth are in fact two surviving letter archives where multiple letters are copied into a scroll and the intermediate openings and closing omitted to save paper, representing perhaps 5-10 letters among perhaps 20 letters or more that Paul might have written to Corinth over the years. 
Second, if the numbers of believers grew from something on the order of 1,000 believers circa 40 CE to over a million by circa 250 CE, a 40% per decade growth rate, optimistically 5%-10% of believers are literate, 1%-2% can write, 0.1%-0.5% can compose original works that can attract the attention of copyists, then by 120 CE there’s about 3,800 believers, 190-380 readers, 38-76 scribes, 4-20 authors … in 250 CE 50,000-100,000 readers, 10,000-20,000 scribes, and 1,000-5,000 authors.
So, yes, some steadfast scribe in Corinth, copying 1st and 2nd Corinthians for those interested in them over two or three decades, similar to other letters of Paul maintained by other faith communities … and, of course, likely a majority of letters of Paul lost to time … and then collected 80-90 CE into a collection of seven letters of Paul which rescues each of those letters from oblivion because now the scribes in all faith communities tracing their Apostolic founding to Paul have an incentive to copy the collection … there’s nothing any less plausible about that than all of the letters of Paul that have survived being in wide circulation in 70 CE and none of the ones that failed to survive, so that the author of the Evangelion eventually attributed to Luke was familiar with exactly those letters of Paul that survived into the third century CE.
  

I made little “argument” in my response.  I stated facts.  The facts are, there was a time when only the Corinthian church knew of what we call 1st Corinthians; the day they received it and read it aloud.

  There is no more fallacy here than saying that there was a time when BruceRmcf was the only one who knew of a letter written to him/her (excluding the author of the letter, of course).

Then there was a point in time when that letter reached other communities.  That is a fact: if what we know as 1st Corinthians never went beyond the household where it originally was kept, we could only know about it via archaeology, literally digging up that household. (assuming it hadn’t disintegrated.)

But we do know about it, and not through archaeology, which means it was copied and circulated throughout Christian communities at least prior to dates when it is quoted among church fathers.

There is literally nothing to argue about in these points.  They are neither controversial nor debatable.  

What I ask is, is it plausible to believe that by 70AD the original letter still sat in a house in Corinth, twenty years after it was received, and had not been copied or circulated?  The only options are: 1) No, within twenty years the letter would have been copied and sent to other christian communities, or, 2) Yes, it is quite plausible that the letter still sat in a home at Corinth at this point and was only copied and disseminated later.

Those are literally your only options (apart from doubting there ever was a real Paul or that the concensus of dates among scholars is completely bogus and 1 Corinthians could easily have been composed in 1874 and Lincoln is a myth and blablabla).