As far as I know, there's no such thing as a back-up lead. Deli, meat, and produce have department heads and back-up department heads. Frozen and dairy just have leads since those departments have so few people working in them compared to deli, meat, and produce.
Here, the back-up is the back-up. They only make higher pay(relief pay which is the same pay as the department manager) when the Department manager is off for the week.
"Deemed by Employer" might suggest the existence of assistant department head positions might vary from store to store.
The Level 4 stuff isn't quite clear to me. Does this provision mandate, for example, one 40-hour position in addition to department heads in the indicated areas?
Would an assistant department head ever be someone other than the Level 4 individual?
I never got it either. All department "heads" in my store are just leads, and get paid according to that level 4 schedule posted above. It seems the "heads" positions making the big bucks just don't exist, and there are no assistants to my knowledge. Backups don't get squat, but they're "next in line" if they don't top out in pay before then (they will).