my guess is that #1 was the only only one with the blue/blue cab. normally the #1 sample is a test sample for engineering. sample games #2 thru XXX were place on location to get info. all the other samples shown on IPDB have red/blue cabinets.
on a side note volley was the largest deviation from sample to production. some games had no changes and some had minor changes. i don't think it really adds to the value but seeing that this most likely the only one made with blue/blue art work i am sure it adds to the value in this case.
i have and had many samples volley is the closest to #1 i got it is #2