Jeff - It was late 1996 or early 1997 that the .999 on the rim was changed to the silver center (thanks to Mark Weavers dealing with the caming commision), and it was in 2005 that the first .05 ounce center started to appear and since then all strikes marked .999 are .05 ounce.
Interesting thing is the other day a seller did his best to make me belive that all the new colorized Blue Cap strikes were again .999 silver and I am sure a few folks are thinking the same thing,
Walt