If you are talking about the WWI Draft Registration Cards then you have the cart before the horse in saying "Soldier's...after registration". The Registration was a civil, not a military requirement of men of a certain age range to file in the county they were living on certain dates (unless they were already enlisted). If you find a card for an ancestor the only thing you know for sure is they were not already in the service. It does not mean they were drafted or served. They could still volunteer if not drafted. If you can find them in the 1930 census, column 30 asks "If a Veteran of Military or Naval Forces" and column 31 usually has WW or SpA and I have even seen CV, if the answer was Yes. (WWI,Spanish American War, Civil War.) Hopefully the census taker filled it in. So those with Cards filed are not yet soldiers.