Damp internal walls on recently damp coursed house

I'm in the process of purchasing a Victorian terraced property in the South Oxfordshire area. In our homebuyers report, the surveyor identified possible damp walls in the living and dining room (knocked through to be one room). This was deemed unusual given that he damp course was done in December 2012. Our survey was done in September 2013. The damp course (chemical injection) invoice mentions the need for re-plastering in February 2013. Is it likely that the vendor waited until September to do this, did it again after February, or that in fact the original course was not done properly and a damp problem has surfaced? Could it also be possible that the cold walls were just due to the property being unheated through the summer months, and not damp at all? We are trying to cut down our queries to reach a completion date and this is one we would like to let go - but don't want an expensive problem on our hands. Does this type of damp course tend to be effective first time? It comes with a 20 year guarantee but only if re-plastering soon after is carried out. Related to this, we plan to install airbricks after we move in to improve the sub floor ventilation. Is this a relatively straightforward job? Many thanks for your help.