We have an agent do our SFP for us as they are so insanely complicated, so my knowledge isn't as full as it would be if I had to do it myself. Although if I did have to do it myself, I would be writing this on the prison computer as I would have long ago taken it out on hapless employees of Defra / RPA.
The entitlements for a given year are applied for in the May for ground you expect to be farming by October (or it might be December) that year. The amount is set at the end of September ('set' because it varies according to the exchnage rate, unless you elect to have it paid in Euros) and paid sometime between December and February, unless there's a really big problem.
If your contract stipulated that the purchase price included the SFP for 2012, then your vendor hopefully claimed for the payment in May and your solicitor is now hopefully arranging for the payment to be sent to you in due course. (My experience is that this will be an excellent excuse for the RPA to delay making your payment until July 2013, at least. And then get it wrong. Which you won't be able to figure out or justify, as they never give sufficient information about what it is they are paying when they pay it.)
If your contract stipulated that the entitlements would be transferred but did not specifically mention the 2012 payment, then your solicitor should be organising for the RPA's records to be updated so that when you make your claim in May 2013, you and the RPA both think that you farm that ground.
I hope that helps.