It's just a marketing thing by the Telegraph .I think they are sent out randomly .We always used to take the Telegraph every day and never received any but my neighbour who has never read it in her life received money off coupons ! We also had a subscription to the Telegraph at one stage and as soon as it ran out and we didn't renew ..hey presto we received some coupons.You could enquire at the Telegraph website but I think it's just a marketing campaign probably and they target different areas at different times.
www.telegraph.co.uk