Do they have the right to issue retroactive adjustment acts?

I currently have a contract with a gas transmission system operator, and they previously sent me an adjustment act due to a tariff change. The court states that if there was an arithmetic error due to changes in legislation, the operator has the right to issue an adjustment act, even if the contract does not explicitly permit it. But my question is: if several months have passed since the original act – can the supplier legally recalculate and charge me an additional payment retroactively after a certain period, and how is this 'reasonable' period for such adjustments determined?