The test results can only reflect comparisons with the reference samples. Ancestry has not, as far as I know, released a description of its reference samples. FTDNA has.
If you have the raw data, you can also upload it to GedMatch and send it to Dr. Doug McDonald for independent analysis. These may show different results. Ancestry has not released the raw data, but FTDNA and 23andMe routinely do so.
Initially, I expected to find (and was disappointed when I did not) that my documented German ancestry would show up. As I've learned more about autosomal DNA, however, I have come to understand that the results on both Ancestry and FTDNA are consistent and correctly reflect my family's origins on both sides. My father's side is Norman-Irish; my mother's is German, specifically Bavaria and Lower Saxony. Celts settled in Bavaria in the first millennium BCE and their descendants are reflected in the DNA results as Orcadian or British. And ditto for the Saxons.
One thing to bear in mind is that autosomal DNA is useful for establishing relatively recent family relationships, but the the ethnic origins results may derive from many hundreds or even thousands of years ago, so one cannot expect to see family origins from only a couple of hundred years ago to reliably show up.