In victorian era abbreviations commonly used were different than today... "Jos" for Joseph.. "Jas" for James.. "Char" or "Charl" for Charles.. "Saml" for Samuel etc... IF a persons name was Joseph.. and written as Jos... it could easily have been confused with Jas.. So you might find two record files one listed as a Joseph Smith.. and another as a James Smith.. which might actually be the same persons record. If a different roll has the person as Joseph L Smith.. then you might find three files.. they had little ability to cross reference if this might have been the same person or not as the previous Joseph Smith.. a cousin, father, uncle etc all using a popular family namesake is commonly found..
Initials.. same thing.. in the old style writting a "T", "J" can look remarkably similar and could easily get confused... If your looking out for a J.Smith.. take a look at the T.Smith too... might be him as well...
Just because a name might match... be cautious that it might or might not be the person your looking for.. duplication of a popular grandfathers name passed down.. sometimes results in several people living (and serving) at the same time sharing the same namesake... which might or might not be part of the same family group your researching.. I always suggest that people do the research on the unit identified with him.. to see what area it was mustered in to see if it relatively matches the area that your ancestor was known to have been from or near... as long as he wasnt a conscript (draftee) he generally would be in a unit mustered from a given area for the most part..
Online geneaology sources might or might not be completely accurate.. Much of it is user submitted. Many times Ive seen people locate a matched name then link that person and his civil war service automaticly without taking the time to research it completely for confirmation.. everyone coming along later taking notes from the same wrong data. Just take it at face value till proven otherwise. Last year I was asked to assist a lady with decyphering "her ancestors" military records.. She was trying to get a SCV marker but needed the documents and confirmation to do so.. she only had a pile of confusing records.. In short.. she had been honoring and visiting a grave of a person whos name matched for about a decade.. yet I found it was actually not her ancestor.. She had even spent the money to buy a grave stone to mark it... She didnt think to check the others buried in the same family plot whom she couldnt find in her family tree should have been a clue.. The grave she marked was a person of the same name.. served well..lived long was buried with his family.. it even was in a distant county that none of her known relatives were even from or had lived in... another missed clue.. Her ancestor.. a conscript had deserted.. needless to say she wasnt happy...
Post-war pension records if any can also assist to further narrow down the searching.. Pension records sometimes include dependents and other useful data to confirm or deny this is the Joe Smith your after... Also in Confederate records if your Joe was originally from and served in a North Carolina Unit... but post war moved to Virginia.. his Pension file would be found in the Virginia pension records... The Southern States basicly had an agreement amoungst them that the soldiers resident state would take care of the pensions of the soldier regardless if he had served there or had served in another southern state unit.
Respects
Frederick