Martin, Thanks for your reply. I agree it does need clarifying if anybody reads it in the future.
This is from ISOGG, page modified Oct 2017, I think it's still correct.
https://isogg.org/wiki/Autosomal_DNA_match_thresholds23andme - For half-identical regions the autosomal threshold is 7 cMs and at least 700 SNPs for the first segment; 5 cMs and 700 SNPs for additional segments and for people you are sharing with. For fully identical regions the threshold is 5 cMs and 500 SNPs.
But limited to 2000 matches
ftDNA - A match is declared if two people share a segment of 9 cM or more, regardless of the number of total shared cM. However, if there’s not a block that’s 9 cM or greater, the minimum of 20 shared cM with a longest block of 7.69 cM applies
(Autosomal DNA uploads from other sites limited to close cousins, more distant cousins only show up for those who test there).
Ancestry - The minimum threshold for a match is set at 6 cMs of IBD sharing across the genome.
Gedmatch - Default set at 7 cM
Again, 'One to many' limited to first 2000 matches.
And from
myheritageDNA site, updated last year -
Previously the minimum of shared DNA for a match was 12 cM and now the minimum is 8 cM.
So only at ancestry would this match show up automatically. I have tried to persuade her to upload to Gedmatch, unsuccessfully, so I have to leave it at that.
A group of Steer descendants from RootsWeb Steer mailing list, have uploaded to Gedmatch, and by lowering the threshold to 1 cM the Surrey Steer group all match, but only by about maximum 4 cM. This is all on the same place on one chromosome, so it is a pity that my ancestry match can't upload there as well, to see how much and where she matches with the others.
We have confirmed the connection between me and her though, so I am happy.
Thanks for correcting me, Martin
Regards Margaret