because their son John (b. Mar 1874) is in the 1900 census of Randolph Twp., St. Francois Co., MO, living with his widowed brother, William, and two other brothers.In the 1900 census, your John (b. Jan 1876) is married and living with his wife in DeSoto, Jefferson Co., MO.I don't see how these can be the same person.Of course, I may be mistaken about the siblings in St. Francois Co., MO, being the sons of George, but they do appear to be.
This is where you really feel the loss of the 1890 census, because if your John was missed in the 1880 census, as it appears he may have been, we lost our best shot at finding him with his parents.I haven't finished extracting the STROUPs from the 1880 Missouri census: http://dgmweb.net/genealogy/Census/StraubEtc/MO/Str-MO-1880.shtmlhttp://dgmweb.net/genealogy/Census/StraubEtc/MO/Str-MO-1880.shtml so there's some hope I may still find him, possibly mis-indexed or skipped by the indexers.
The other possibility is that, in the 1880 census, he went by his other given name, not John.In the 19th-Century, people have a habit of switching between their first name and middle name from census to census, much more often than we would ever do.This is particularly true for Germans.
The English tradition, the one that we use, is that your first name is your "call name."The German tradition is that your first name is your saint's name, and your middle name is your call name, so you are much more likely to see a switch between the two given names in records.It doesn't help that Johann/John is by far the most popular saint's name for a male, so it's *the* most common male given name for STROUPs.
Sorry I couldn't be more help.As I mentioned, if you have a male STROUP relative, you can have him DNA tested, so you at least know to which STROUP family you belong.