Just to be clear, if one acquires Silver status on 1st of the month, then the new membership year will end 8th of the month 13 months later and failure to maintain status or be promoted will result in demotion at the end of the month 14 months later?

E.g.
Status acquired 1st November 2012.
Membership year ends 8th December 2013.
Demotion (insufficient TPs) occurs 30th January 2013.

I am planning strategies to acquire Silver under the new Avios 'multi-scheme'. <regional UK>-LHR-MAD-<regional Spain>-MAD-LHR-<regional UK> in CE looks a good run.