I recently picked up a copy of MOSAICS by Michael Rabin on Capitol (stereo) at an estate sale. When I checked the lp on popsike, I noticed Ebay sales prices going from $500 to $5000 over the last few years. Because many of these seem to be advertised in similar condition, I'm confused as to why the big swing in prices. Is there any particular thing (stamper, matrix, etc) that would differenciate a more rare copy from a more common one? I appreciate the feedback.