As far as I know, none of the RV kits are "serialized" (Except for the RV-12 when built as E-LSA). You are assigned a serial number of "plans", but you are not obligated to use that S/N.
In the beginning, the fuselage center section and wing spars were serialized because they were "match drilled", but that is no longer a factor, with the possible exception of the -3, -4 and -6.
You may assign any serial number to your aircraft as long as you have not used the same serial number on another aircraft.
The "official" date of manufacture of your airplane will be the date the airworthiness certificate is issued.