To each purchaser of a ticket to the Grand Avenue Park when a League game is to be played, the St. Louis Base Ball Association furnishes a coupon on which is printed the following:"If rain prevents the playing of five innings this coupon will be redeemed on presentation at ticket office."This is a move which can not be too highly commended, and is one which will bear following by all organizations throughout the country. It will, without doubt, pay in the long run. On this subject, the Chicago Tribune justly says: "The St. Louis Brown Stocking management have determined that, when a game at Grand Avenue Park hereafter shall be interrupted by rain before the end of the fifth inning, they will refund the admission money to the spectators. This is an honest policy, and the managers make themselves deserving of a warm support from St. Louis people."
-St. Louis Globe-Democrat, July 27, 1876
William Spink had championed an "honest" rain check policy since the beginning of the season and should be given some credit for the practice being adopted in St. Louis in 1876.
This could be somewhat significant if we're looking at the history of rain checks. I think that what the Brown Stockings were doing fits the definition of a rain check that Morris uses in A Game of Inches. The best Morris offers, with regards to the beginning of their use, is that they were being used before March of 1881. We now have specific evidence of their use in 1876.
I'm not suggesting that Spink and the Brown Stockings be given credit for the invention of the rain check because I don't know enough about the subject to say that. However, if the history of rain checks ever comes up for discussion, they should certainly be mentioned among the pioneers of the idea.