The S.O.P. they signed acknowledging they were aware management could no longer enforce the tip-out (which I believe is simply evidence of their knowledge of the contract, the actual contract would be implied from circumstance and based on testimony of co-workers). There are other SOPs that may be relevant too, like one stating barbacks must be present while tips are counted and distributed (which may not be contradicted by the previously mentioned SOP, but which the bartenders refused to allow anyway), but I'll need to check with human resources before I go any further with that.
Is signing a lease on an apartment with pay stubs and bank statements attached to show my income in tips in order to get approved, when I previously lived with my parents and did not pay rent, not considered changing my circumstance in response to the (assumed) promise?
Can you provide any more information on promissory estoppel in Ohio small claims courts?
Edit: I should add that some instances of under-tipping are also under investigation by human resources, and these cases are attested to by other bartenders who divulged what they made that night and that the bartender in question did not tip the barbacks at the recommended rate.

