Shared match oddity

[Petros]

I have one pair of shared matches S (24 cM) and A (20 cM). A has no tree while S has a  large tree in which I recognise no names.

These two only show as shared matches with each other. However, I keep seeing new matches which show as shared with both A and S!

Any rational explanations?

[haliared]

1. S could be adopted and still a match to A. Or vice versa.
2. S could be biologically unrelated to the people on the linked tree, if it is the tree of their adopted family for instance.
3. S may not even be the person who is showing as the home person, or even a relative of the linked tree.

[Cas (stallc)]

I have one pair of shared matches S (24 cM) and A (20 cM). A has no tree while S has a  large tree in which I recognise no names.

These two only show as shared matches with each other. However, I keep seeing new matches which show as shared with both A and S!

Any rational explanations?

Are the matches below 20cM? Ancestry (not sure of others) only show shared matches if at 20cM and above.

Cas

[brigidmac]

Have you checked S s spouse  click on spouse of home person + their parents may appear .but not names of ALL the ancestors. Couples often take DNA tests and link them to trees but only research one side of the family

Or have a branch that they keep hidden  because they know it is a biological line .
 there COULD be  a non bio relationship that they don't know about so surnames won't help .
Look for connections to locations instead.these could be really distant relations 20cm is quite low

Cas ancestry does show some mutual matches of less than 20cm sometimes.

[4b2]

20/4cM is a very ambiguous amount. It could be a more distant relationship. If the person has gaps in their tree going back to about 1720-50, open the profile for those dead ends and press the search button at the top of the profile. Often you will find a continuation of the line in another tree.

If there is no apparent link it can be worth noting the locations of birth. I have some matches with no link in the tree in the time-frame it should occur, but then you see one person in the tree was born in a place overlapping your lines. If there are enough closely related matches you can sometimes get a good idea if there was infidelity or the bastardy. I have half-solved several others' NPEs by going through all my matches and locating such occurrences.

But there could be any number of issues, like what others have mentioned. As someone noted people can link the wrong person in the tree. Often a spouse. When the tree looks like there is no connection I look to see if there is a tree of the spouse. You can use the origins/ethnicity to get an idea if they may have linked the wrong person. e.g. if the ethnicity says half-Scandi and half-Italian, yet the tree is all in England, then they've obviously linked the wrong person.

[Petros]

I think you are all missing my point

A&S are shared matches only with each other and me BUT I have around a dozen matches whose only shared matches are A & S, but but none show as shared matches for either A or S

[brigidmac]

Sorry that last paragraph doesn't make sense to me

Did you give the cm amounts and are they from 1 parents side or  .both ..it's really not worth investigating if under 30cm  have to wait for more matches to come in

[aghadowey]

I think you are all missing my point

A&S are shared matches only with each other and me BUT I have around a dozen matches whose only shared matches are A & S, but but none show as shared matches for either A or S

Just wondering if the reason is those dozen or so matches share very low cM % with A and S. On My Heritage it shows not just mutual matches but those that match on the same chromosome(s) which can be helpful. I also use DNA Painter to figure out mutual relationships.