Ah, nice. Yeah, get some paraffin wax and rub it on the rails and the slots on the drawers that ride on the rails. That'll make the drawers very smooth to operate.
I think that joinery you would call rabbet and dado, as oppose to tongue and grove.
Tongue and groove and when the joinery is on the long edges. Like paneling or flooring.
Dovetail is actually more common to find these days for drawer construction. Given the age, this might have been handmade and that joinery might have been hand cut. Hard to say from the one pic. Dovetail is definitely a superior joinery for drawers. You can see in the pic, there's just a small bit of wood on the outside part of the dado. It's easy for that to break off. Which is typically why you try and avoid putting a dado on the edge like that, and why dovetail is superior for drawers. But if you were hand making these in a production settings, it would behoove you to to use a joinery method that's faster and easier. That's why the triangle thing is there. It's to reinforce it. If it has a proper name, I can't think of it right now. Maybe a gusset? But gluing that triangle piece in definitely helps to keep that corner strong and keep it from breaking. The proof that it did its job is that all four drawers lasted this long without any of them breaking. So if it sounds like I'm being snobby about dovetails vs rabbet/dado, I'm not. I like it!
But here's what a dovetail drawer looks like...
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