It is outsourced and has been for years (Withdean) i worked for the company that handles it for 4 years. From memory these delays have been associated since the move to the AMEX (certainly the last 2 seasons) and the database (a much larger one) took longer to arrive from the club.
The actual...
They don't (or never used to) have their own postage account so it they would the Mailing Houses account instead. Obviously the larger the quantity posted at any one time would secure the largest discount so there fore they will all be posted as a batch.
Unless things have changed and it's all...
I heard something along those lines either the ticketing or the cust services have been relocated to the Overline office in Worthing. Regarding the posting of the actual season tickets that is also outsourced and had been since the later Withdean years (I worked for that company for 4 years)...