So this is the information that I have gathered. I think it is fairly accurate.
(1) SG on the front Pre 1999
(2) SGC on the front minus 1-10 grade 1999 thru 2004
(3) SGC on the front plus 1-10 grade plus gold label on the back 2005 thru 2008
(4) SGC on the front plus 1-10 grade plus SGC pressed into the back 2009 thru Current