This is a tricky area and the FDCPA should actually be amended to be clearer on this issue. While the Fair Debt Collection Practices Act states that the consumer should dispute the debt within the first 30 days of receiving the notice it does not state that one cannot dispute it later. It may be that one has discovered the debt 45 days later or the original notice sent by the collector did not reach its destination or that it was received but unaddressed. Either way, there is NO provision in the Act that says one is barred from disputing later, it may just take more persistence, more money, and a countersuit if the debt collector goes to court for a judgment.
If the collection agency completely refuses to validate one's debt because they claim it has surpassed the 30 day period then their only other option is to sue, wherein one can defend themselves by appearing and explaining to the court proof was never received and that there is a refusal to pay anything until validated. Additionally, the collector will not be able to prove when all parties were first notified of the debt simply by sending a notice in regular mail. What if the letter never arrived at its destination?
History shows us that collectors HATE Validation of Debts requests. It is time-consuming and stalls their collection efforts. Most never even receive the proof even after many requests. Many consumers never hear from the collector again after they ask for the Validation Of Debts. If the balance is large enough and worth the collector's time, one may receive some sort of proof but it is not legally validation.