When I got my Outpatients Appointment letters they arrived in six envelopes over two days.
Now, you'd have thought that someone booking these knew they wanted a recurring appointment, on the same day each week for 6 weeks (albeit not all at the same time but near). How difficult would it have been to make 6 appointments and put them all on one letter? Everything would have been in one place, the cost of letters, envelopes, handling and postage alone would have (you would have thought) paid for the difficulty of doing that.
I reckon though that the computer system cannot do this and each appointment once made automatically generates a letter.