These are my notes that I have gotten off this site. They have helped me a lot.
1964 & earlier are 90% silver 1965-1970 are 40% silver.
1966 (FG designers initials missing from back)
1974D double-die at the RUS in TRUST.
1971D some were 40% silver
1976S is 40% Silver half
1977D some were 40% silver
1982 (FG designers initials missing from back) worth $3.00-$5.00
1983 (FG designers initials missing from back) worth $3.00-$5.00
1987-P or D (only issued in uncirculated mint sets - S is from proof set)
1990 (FG designers initials missing from back) worth $3.00-$5.00
2002-P or D (only issued in uncirculated mint sets - S is from proof set)
2003-P or D (only issued in uncirculated mint sets - S is from proof set)
2004-P or D (only issued in uncirculated mint sets - S is from proof set)
2005-P or D (only issued in uncirculated mint sets - S is from proof set)
2006-P or D (only issued in uncirculated mint sets - S is from proof set)