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Question on Aspirin Back titration on the Nuffield Chemistry React site

On this page: http://www.chemistry-react.org/go/default/Tutorial/Tutorial_21681.html
it talks a bit about back titration. If you scroll down you'll find it says:

As with earlier techniques, this procedure is most simply used for aspirin tablets, but could theoretically be adapted as described earlier for laboratory samples of aspirin, in which the main impurity, 2-hydroxybenzoic acid, will obviously interfere with the procedure.

However, call me dumb, but why would the 2-hydroxybenzoic acid impurities interfere with the procedure? XD Is it just because it's an acid and therefore more NaOH is needed to neutralise it? Would this affect any calculations and whatnot in any way?