Following some confusion on Facebook site I checked with Mark Hornby who says
A letter was sent to 18/19 Season Ticket holders who have not renewed and should be landing around now - the discrepancy may come if they bought this season using a different supporter number/profile that the one that they used in the 18/19 Season. If an individual has a query on that, they can contact the ticket office (ticketoffice@ccfc.co.uk) who will be able to double check for them.