On Sept 4, 2014, Roberta Estes of DNA-Explained.com posted the following blog:
"What Does and Doesn’t a Y DNA Match Mean?"

(URL = http://dna-explained.com/2014/09/04/what-does-and-doesnt-a-y-dna-match-mean/)

In it, she revealed a number of Y-DNA Match parameters accepted amongst the
expert community.  For convenience sake, I excerpted/edited the article to list them:



MATCH THRESHOLD
We each have results for each panel: Y-DNA12, Y-DNA25, Y-DNA37, Y-DNA67, or Y-DNA111.  
Do STRs match exactly between two persons?  The number of differences in a given panel
tells if the match is genealogically relevant.  This is the Match Threshold:

Markers in Panel Tested		Maximum Number of Mutations Allowed 
12				0 unless in a common project, then 1 
25				2 
37				4 
67				7 
111				10 

The reason for these thresholds is that DNA mutates at an “average” rate and for someone 
to have more than this number of mutations in that marker range means, generally, that 
the match is too far back in time to be genealogically relevant (within 500-800 years ago).

If you match, use FTDNA.com’s TIP calculator to estimate of how distant the most recent 
common ancestor (MRCA) is from you and your match.

LET ME INSERT HERE THAT, FOR L1 VINCENTS, OUR FARTHEST MRCA IS JOHN VINCENT (D.1698). A 
DIFFERENCE IN ONE MARKER BACK FROM HIM, (MORE THAN 300 YEARS AGO) FOR US, WOULD BE AN 
UNKNOWN ANCESTOR BUT STILL NAMED "VINCENT" OR "VINSON."  YDNA PROOF OF AN ANCESTOR MORE 
THAN 800 YEARS AGO WOULD PROBABLY MEAN THAT ANCESTOR HAD A DIFFERENT SURNAME OR NO SURNAME.

- 12 markers is not sufficient to determine a common ancestor. You should upgrade.
- yDNA testing can only tell THAT we match, NOT how close a cousin we are except, maybe 111.
  Only Family Finder & genealogy research CAN tell how close a cousin we are; 5 generations
  for Family Finder, 11 generations (so far for Vinson/Vincents) through genealogy research.
  [I WOULD ADD HERE THAT COUSIN JOHN VINCENT AND I WOULD NOT MATCH ON A FAMILY FINDER TEST.]
- The pattern of STR markers is what determines a match, not individual markers.  For example,
  we can say with some certainty that, if DYS455=8, you are probably an I1.  There is no 
  particular STR marker we can point to that tells us "you are a Vincent."  It's the PATTERN
  of STR mutations that tells if you are Vinson/Vincent.