Adjusted Annual Return of Withheld Federal Income Tax or Claim for Refund
Form 945-X corrects a previously filed Form 945. It matters most where backup withholding was misreported, because the amount also appears on the information returns issued to those payees - a correction here usually means corrected 1099s as well.
Whether you deposit monthly or semiweekly depends on your lookback period, not on this form. Publication 15 (Circular E) sets the rule, and it is worth checking each year - the schedule can change when your liability does.
IRS Publication 15Usually yes. The withheld amount appears in box 4 of the information return as well, so the payee's copy needs to agree with what you have now reported.