Ancestry.com has the image of the WWI Card you can print or order an enhanced copy from them, same with the scanned death certificate and U.S. Army Enlistments at ages 20 yr and 10 mos and age 25. Honorable Discharge March 1912 from CAC unit -Coast Artillery Corps. Issac even noted on his WWI Draft Registration Card he had 6 yrs with CAA going from Pvt to Corporal at bottom question asking about prior military service. The NARA has all WWI Military Records http://www.archives.govhttp://www.archives.gov
You cannot change a death certificate as filed with a county.(you could try to file an amended one if they would let you for one in 1925 so long ago) The website you are seeing the scanned image online should have a "add comment" link, at least Ancestry does. Click on it and state the informant on his dc reported the wrong first name of his mother. Then note the correct name Rachel and that Nancy was first name of second wife of father Allen.