The point everyone seems to be missing is that if the treads are pocketed into the stringers, in the traditional style, then the pockets are not parallel top & bottom, they are slightly 'triangular' & shimmed from underneath.
This means that no amount of glueing & screwing from the top will prevent the rear of each tread from sinking with additional weight. By the time you've rammed enough screws in it to hold it still, you're never going to look good if you try to stain/varnish it.
Think pincushion.
The art of the traditional staircase is you can't see the nail-holes. It's all underneath. You trim it back to spec simply by tapping the shims tight again. Sure, these days it wouldn't go amiss to add some glue to that. You might even try screwing each riser to its lower tread, which would probably not have been done originally… ironically, to prevent squeaks.
Note the risers do not sit on the tread below, they hang behind.
Only photo I could find. Seems no-one wants to build them this way any more.
