Jim,
I think Ed R and I use the same #19 brad and not Atlas nails. I leave my brads in and I think Ed R does also. The head of the brad disappears after painting the track.
I do not deliberately leave my track unballasted for years. It just works out that way. I do put the glue between the ties on the curves as soon as possible after laying the track. Generally, not more than a day or two elapses before I do it.
Ed
P.S.: Ed R gave me the tip on using #19 brads years ago. Thanks again Ed R.