Any revisions to the May 1, 2013 499Q (projecting Q3 revenues) must be filed with USAC no later than June 15. If you discover an error in the 499Q and fail to revise it within this 45 day timeframe, the Federal USF invoices for Q3 will reflect the original 499Q filing and (with very limited exceptions) must be paid in full to avoid red light status and costly late payment penalties.
Other than an appeal to USAC or the FCC (which generally aren’t successful), the only way to correct an error after the 45 day revision deadline is through next year’s April 1st 499A, when you file actual 2013 revenues. Keep in mind that the 499A true up methodology includes an implicit penalty for over or under projections made on the 499Qs. Bottom line — be as accurate as possible when filing projected revenues on the 499Q and fix any errors within the 45 day revision period.