A death notice is usually something published in a newspaper. FindaGrave is a user-created database of burials, usually without sources. In Harry's case, it shows his headstone with complete dates, which is certainly a good thing.
You have Harry and Shirley's marriage record, which shows Harry's parents' names. (By the way, that record is on Samuel's profile, but it should be on Harry's as a source.) So you probably have the correct names of Harry's parents, even if you haven't found records that match them.