Another point about your pricing vendor, on Scott number 2216 (sheet of 9 President stamps) they have a sheet value. They value it at 5.70 where the street places a value of 10.00 on it (them). The rest of the series 2217, 2218, and 2219 they do not mention sheet in the values. That mean the next price update the value of the stamps will drop to zero, because the description says sheet and the item value does not have a sheet value. In a lot of cases the value of a block of four stamps is closer to being the current street value for a single stamp of the block.