Hi,
Assuming that what you have is Scott RJA42b, rouletted 7 on watermarked paper, then you're looking at a value of about $50 (200 * .25).
These panes are not too hard to come by, and I doubt that you could find someone willing to pay a premium for it.
So, it's real, market or trade value is probably $25 to $40, but if you stick it up on
ebay you may it sell it for far more.
Jim