I don't believe a receipt is totally necessary. You are allowed to use a previous year's kitbot frame
IF is composed of parts that are still available from the companies that provided them. These parts would just need to be properly spec'd and accounted for on the teams BOM (Bill of Materials, for you rookies
).
HOWEVER, parts from previous years kits that are no longer commercially available to all teams
OR are not legal by all rules that pertain to the robot may
NOT be used.
Hope that clears some things up.
EDIT:
For anyone trying to find part numbers or prices of previous year kit parts link is below.
http://ifirobotics.com/kitbot.shtml