Looks to be a dedicated mulching deck. No cut-out for discharge that I can see. Cogged belts are common on decks with over lapping blades. The cogs are to keep it in time.
Discharge is across the back. There is a worn rubber deflector there. I don't think the blade actually overlap in their travel. I will check tomorrow. (the pulleys are not toothed)
When you say toothed do you mean like a timing belt or just a cogged belt. If the pulleys are small they most likely used a cogged belt as it will last longer.
All replies appreciated. This one is a puzzle. Gearbox looks like a John Deer f725 but no other similarities. Heavy machine at 100kg plus. Looks like a substantial maker but nothing online at all like it