There is a really huge price gap in the 1963P Quarter

Sales of NCG graded 1963P quarters at Heritage in MS-67 have been:

$205 on 3/6/06

$276 on 3/28/05

$241 on 5/5/03

$201 on 4/8/03

$258 on 3/3/03

$213 on 3/3/03 and

$235 on 1/13/03

while PCGS coins have sold for:

$2530 on 1/15/05

$3680 on 11/6/04

$3220 on 6/5/04 and

$3450 on 11/7/03.

Is this typical? What is the explanation for this difference?