Servers Lying And Underreporting Bar Sales To Minimize Tip-out

It was just brought to my attention that servers at my restaurant have been shorting tip-out numbers and this has been going on for years. Basically, servers check out and declare what their bar sales were, and the bar (me) gets tipped out a percentage of those sales. It was recently discovered that many of the declared numbers (by the servers, not checked by management) were inaccurate, and the servers were tipping out less as a result. There is a paper trail of this that goes back years. It's my understanding that in my state (California), the company is unable to punish financially for these errors, but I am wondering if I have any recompense via civil court or if there is any other avenue I should pursue.

The tip-out percentage is mandatory and agreed to upon employment, and the errors were simply a result of the servers lying and making up lower numbers to avoid tipping out the agreed-upon amount. I'm honestly aghast and wondering what my next moves are.