Is anyone familiar with the 2003 Donruss Heroes "MASTER SET" parallels? I know that the cards are numbered /20, with #1-10 being gold and #11-20 silver.

However has anyone ever heard of the "MASTER TEAM SET" numbered /15? I just picked up some of these and didn't see them listed in Beckett. They're identical other than the serial number to 15 instead of 20.

Can anyone provide some background on these for me? Thanks!