Statute of Limitations for Lease issue

Client is landlord who has a lease with a provision that requires the tenant to pay for certain expenses relative to the property. Tenant only pays a portion of any annual increase from the base year amount. Base year is 2010 when expenses were about $3,000 but tenant has not been taking advantage of applying the base year to reduce its expense. Client just found about the possible error and not sure why tenant did not apply the base year. Client's fear is that if they extend the lease for another 5 years, tenant might discover the situation and attempt to recover--maximum recovery would be $3,000 per year for last 10-11 years. There are other mitigating circumstances but I only want a review how far back the tenant can go. It is a situation where each year there has been a loss to the tenant---so I am not clear if the event triggering the damage is the annual payment (which is larger than should be) and since it is a written contract they can only go back 4 years or if they go all the way back to 2010.