Individuals are very often entitled to awards in addition to those listed on their respective discharge/separation documents. (see Message #4075). This is most commonly due to the awards process itself. A recommendation would be submitted and processed through channels and could take anyhere from six months to a couple years to be approved. It might be another three to six months before it was actually conferred, by which time the awardee is no longer in service.
Awards authorized or awarded subsequent to the individual's release from active duty very often went unrecorded - the individual's service record had been retired to a records center and the services - especially the army - refused to bother with amending individual records.
Those at FPRC St. Louis aren't as concientious or attentive as they once were. But consider also that they've been deluged with requests for medals that no one even thought of - much less asked for - in fifty years or more. Also, unless you have official verification, FPRC usually issues only those awards listed on the individual's discharge/separation papers.
I can determine other awards an individual may be entitled to but I need dates of service and other info. I can also furnish these very reasonably, eliminating the often lengthy process of amending records and waiting to actually receive the awards.