It might be important to note that the cheque is usually valid for 6 months from the date 'on' the cheque, not the date it was 'sent' as your question specifies. However, many cheques for share dividends are valid for a year but this is specifically written on the cheque itself. Also, if the cheque or draft is drawn on the bank/building society itself, it sometimes can be validated for a longer period.
i was told by a bank that pre dating cheques isnt allowed, and if you paid in a cheque that was dated for, say, the next week they would pay it anyway.