Communidad Fees when selling a flat.

We are selling our flat in Barcelona. We have large bills to the communidad for major reforms and have agreed with the buyers to split the costs. When we asked for the final certificate, the management company said that they need to include and additional cost which has not yet been assessed (but was approved in 2009--another owner did structural reforms and the commuity agreed to pay). This amount has not yet been officially assessed but they say it needs to be included. Is this correct. The signing of deeds is on 29 May and the amount will not be officially placed on anyone else's bill by then.