'69 L.A. Cars: There was never anything on the cowl tag to indicate if it was a Z/28 or an RS, and X-codes were never used on L.A. cars. You have to use other "clues" to determine if it was originally a Z/28 or an RS, or both.
'69 Norwood Cars: Prior to X-codes, same as above. After X-codes (12B), Z/28's were either X33 (with style trim) or X77 (without stlye trim). There was no code on the cowl tag for RS. If a Z/28 was also an RS, it had to be an X33, as RS included style trim.