Creating those historic prices was a right bit of hard work! So I've only done it for coins in my collection, but luckily I've got all the relevant Seaby/Spinks for the years listed.
The 1861 F23 proof was:
Struck in January 1861 as part of an experiment to determine whether the weight standard of the new bronze coins should be altered in order to coin 40 instead of 48 pieces to the pound avoirdupois