Yeah I had never noticed they were not there before.
The tractor had the original blades on it until this spring when I ordered a set of Meg-Mo's for it. I'd been thinking something wasn't quite right and had chalked it up to the old blades being worn out. I was going to hunt down new jam nuts and washers for the spindles since the originals are kinda long in the tooth so I suppose I'll just get 6 washers instead of 3 now.
Thanks guys!