Can punctuation or spaces be used in a check number?
No, punctuation or spaces should never be used in a check number. You may use numbers or a combination of numbers and letters in a check number.
Occasionally you have unused check stock that you want to use, but that has been voided (usually because the number was assigned in error) in the software. Since check numbers must be unique, to use the check stock, add an alpha character at the end of the check number.
EFT check or ACH check numbering suggestions. EFT+date+alpha EFT201712A, EFT201712B, for a 1/2/2017 date...
By entering the year first you will have all checks for the same year together by check number as opposed to all checks for the same month regardless of year.