Ligated Vector Age - When is a ligated vector too old to use? (Jan/27/2010 )

Does anyone know if there is a broadly accepted "best if used by" date for a ligated vector? I have a set of pCR 2.1 ® ligations (that is, I have already completed my ligation reaction...insert is presumably......inserted) that I would like to revisit but am unsure if they are too old to be successful during transformation. They have been at -20 degrees for six months now....too old? Thanks everyone!

How long after the ligation reaction were the tubes frozen? Theoretically, there's no "best before" date if the samples were frozen, but there's only one way to find out... do the experiment.