With respect to 25/100% I just came across something; the white paper referenced in bread 1328 states on page 10 that 23&me uses only the Y chromosome due to some issues with the X. If they are looking for carriers of a particular line up close, that bloodline could show up as 25/100%. Link to the white paper:

https: //permalinks.23andme.com/pdf/23-14_admixture_date_estimator.pdf