Another problem is Sephardic.
Full Sephardic Jews only score ca. 7% Ashkenazi in JTest (not even close to 26%).
Contrary to stereotypes, a lot of Jews in Northern Europe were actually Sephardic.
Recently I learned, that German Jews can be not only Ashkenazi but also Sephardic:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1682349/pdf/ajhg00053-0238a.pdf
"Sephardic Jews in Germany
In the 1930s when German Jews were trying to obtain
immigration visas to other countries to escape Nazi
persecution, they were told at Spanish consulates in
Germany that, if they could prove they were descended
from Iberian Jews who had been expelled from Spain or
Spanish Portugal after 1492, then they were very welcome
to return to the land of their forebears. Even as
late as the 20th century, many German Jews were aware
that one or more of their ancestors had come from the
Iberian Peninsula; for example, the head of the Ullstein
publishing house, Leopold Ullstein, the banker Max
Warburg, the shipping magnate Albert Ballin, as well as
the great German poet Heinrich Heine were able to
trace their ancestry back to one or more Jews born in
Seville, Lisbon, Porto, Toledo, and elsewhere (Kruse
and Engelmann 1992).
There were about 300,000 Jews
in Spain and Portugal in 1490 (Baron 1967) who had to
either emigrate or become Christians; the majority emigrated
and settled, at least temporarily, in Muslim
countries. In 1490 there were about 80,000 Jews in the
Holy Roman Empire, i.e., Germany, Austria, the Low
Countries, and Switzerland. When Protestantism became
victorious in the north of the Holy Roman Empire,
many Sephardic Jews left the Muslim countries, as
well as France and Italy (especially Venice), for the
north, at the invitation of the Protestant rulers there.
Since they had knowledge of the Arabic number system,
the most advanced Arabic medical practices, and,
usually, more than three or four languages, they were
very welcome as physicians, jurists, bankers, and tradesmen.
Even if only 10% of the original Iberian Jews
went to Germany (many via Amsterdam, Venice, or
Antwerp), they constituted in 1648 about 30% of the
Jewish population. Since their standard of living and
their practice of most medical advances were much superior
to those of the Ashkenazi Jews, their percentage
in the German Jewry must have increased until the German
Jewry were emancipated circa 1848.
A survey conducted recently by myself among
readers of the German-Jewish New York weekly AUFBAU
revealed that a substantial number of its readers
knew that they were descendants of Iberian Jews who
had settled in diverse regions of Germany under Protestant
control.
Thus it seems advisable that, in genetic
studies on gene geography, studies comparing Sephardic
with Ashkenazi Jews should not include German
Jews among the latter."