What about first names of those ancestors whose surname ends in -at? Do you find your ancestor’s name/s in this list from Germany?
By the 1880s name-giving changed remarkably from the earlier favored Old Testament. For example, in 1884, in Gorlitz, Germany, the following preferences were noted:
Paul 14.5% Otto 3.6%
Max 11.3 Arthur 3.6
Richard 6.0 Gustav 3.3
Carl 5.6 Fritz 3.0
Alfred 4.0 Georg 3.0
Bruno 4.0 Hans 1.9
Other masculine names used occasionally were Hermann, Curt, Ernst, Oskar, Robert, Adolf, Emil, and Hugo.
What about feminine names? The most frequently names used in Gorlitz, Germany, in the late 19th century included:
Anna 12.0% Bertha 4.3%
Martha 10.0 Margaretha 4.2
Emma 7.3 Helene 4.0
Maria 6.5 Hedwig 3.8
Clara 6.0 Ida 3.4
Elizabeth (Elise) 5.5
Some other popular feminine names included Gertrude, Selma, Agnes, Alma, Minna, Luise, Frida, Meta, Lina, Olga, Auguste, and Pauline. 
If you find ther first name/s of your –at ancestor/s in the above lists, this may be another indication that these -at families considered themselves German.
Some examples from the work of William Hoffman and George Heron:
Adolf: “adol” means “noble + wolf.” Obviously, the popularity of this name has plummeted since World War II.
Pauline: feminine derivative of Paul which means “of or belonging to Paul.”
Josef: masculine from the Hebrew language which means “God will add.” This is a reference to Joseph, the son of Jacob and Rachel.
Amelia: Germanic, feminine name which is a short form of Amalberg. “Amal” means “brave, valiant, hard-working” plus a reference to the Gothic Royal Family Amala. Variations include Emalia and Emelia.
William: Germanic, masculine, compound name. Will (Wil) + helmet (helm) which means strong-willed, helmeted fighter.
Wilhelmina: feminine version of William (Wilhelm in German).
Because the choice of names was rather limited, it is very common to find several people, even in the same immediate family, with the identical first name. To avoid confusion, researchers must carefully check the names of each parent and the birthdates of individuals with the same name to make sure that the correct lineage is being followed.
 Smith and Smith, Encyclopedia of German American Genealogical Research, 100.
 William F, Hoffman and George W. Helon, First Names of the Polish Commonwealth: Origins and Meanings, (Chicago, Illinois: Polish Genealogical Society of America, 1998), 66.
 Hoffman and Helon, 279.
 Hoffman and Helon, 198.
 Hoffman and Helon, 75.
 Hoffman and Helon, 346.
 Hoffman and Helon, 347.