But changes that Uber made to its contract in 2015 suggest that the company has been aware of the issue and grappling with it since at least that year.

In an update to its contract in November 2014, Uber said that it would levy its commission on the pretax or “net” fare. If cities or other jurisdictions “require taxes to be imputed in the fare, Uber shall calculate the service fee based on the fare net of such taxes,” the contract stipulated.

In December 2015, however, Uber changed this portion of the contract, replacing the phrase “imputed in the fare” with the phrase “calculated on the fare.” The new wording, while ambiguous, lent itself more strongly to an interpretation that the fare did not include taxes.

That appeared to address the problem that Uber admitted to last week: computing a commission on a tax-inclusive fare. But whatever legal cover that might have provided, the company did not change its practices until now, continuing to base its commission on the full fare while telling passengers it included tax. (The company continued to remit the tax revenue to the state.)

Richard Emery, a plaintiffs’ lawyer who litigated a 2009 case with similar issues, said the change in the contract was “very powerful circumstantial evidence that they understood that their calculation of the commission was wrong.”