What happens when the app adds additional comparisons to a "Confirm cousin" or "Possible triangulation" card?
The following behavior has been observed by users:
After clicking on a "Confirm cousin" card, the program begins performing comparisons until only 1 is left and then starts again with new comparisons.
When this happens, a lot of matches occur in some areas of your genome. These areas are sometimes known as pile-ups, and companies such as Ancestry limit the number of matches in these areas.
These areas usually result from a shared ancestor, who had many children who, in turn, had more children, who, in turn, had more children of their own. This leads to a very large number of people with the same ancestral DNA, which leads to many DNA matches.
One of the problems of all genetic genealogy companies or apps is the size of their data. Not only because each user has nowadays thousands of matches (some even in the tens of thousands) but they need all to be compared to each other.
While this is no problem with 4 people (resulting in 6 comparisons) it goes up to 10 comparisons for 5 people, 15 comparisons for 6 people, 21 comparisons for 7 people, and so on. 50 matches require 1225 comparisons, 100 matches require four times that, 4995 comparisons.
As our app needs to keep track of which comparisons have been done already and which not, we need to manage the size of the database, as it influences our operating cost directly. This is why you see on some cards that new comparisons are added as soon as they have finished all the previous ones.
Because we don't know which comparison might be the one that leads us to a new MRCA (remember we're looking for a 1st or 2nd cousin connection between all mismatches), we must examine each and every one. They are also determining if a match becomes a DNA cousin and is added to a triangulated group.