Greetings from Afghanistan!
Your S1 is correct about double tapping, plus the fact that there are two types of military education codes: “Correspondence CRS Total # Hrs” and correspondence/distant learning.
When a resident course code is used, the course name and year completed is listed under Section VI of the ERB. When a correspondence/distant learning course is used, the course name and year will not appear, however the “Correspondence CRS Total # Hrs” will update with the appropriate number of hours. So if your S1 were to use a “resident course code” for a correspondence course, they would be absolutely wrong.