Is that standard fitment on earlier axles? I did my front brakes on my 1990 90 a couple of years ago and took off the bolts but not spring washers, someone chucked them I guess. I do remember doing my copper slip locktite trick with them though.
A little copperslip at the top but not onto the threaded area to help the flanged bolt rotate on the disc and top stop if corroding, and the smallest drop of locktite, which has always worked but if spring washers ought to be there, then fit next time I shall.
Mind you, I am fitting a new axle soon which comes complete with brakes so with any luck they are put together properly anyway!