In that case, either you don't recall correctly, or you are owed that money. There's no contractual basis to exclude any company-directed travel from per diem payments.

I got per diem during IOE (to include my OBS trip). Indeed, classmates of mine who had their sims in MIA got per diem before they ever even saw an airplane. I recommend you check your pay statements carefully, and follow up for any missing trip(s)....