Spreebooks expire in the October of the following year after they were issued. So if you have a 2011-12 Spreebook it expired on 1 October 2012 and if you have a 2012-13 one it will be valid until 1 October 2013.
You can find this and other information on the Spreebook facebook page here. If you look under 'Your Spreebook' you will find a link about 'When does my spreebook expire?' You may like to explore the other FAQs too.
If you want to find out more, or if you think there may be an exception in your case or just want them to explain how this works, you could go directly to the Spreebook website. If you go through the Contact tab you will find the same list of FAQs, but also a phone number you can call during office hours. The company have offices in Aberdeen and Norwich.