For direct use as template in PCR runs. Chelex 100 5-10% w/v extraction. Without listing the whole protocol, in the end the supernate is decanted off and then stored at 4°C. I was under the impression that this could be stored and later used almost indefinately but two of four samples extracted several months back failed to produce a product (when it was known they should have).
Assuming no mistakes were made and the reactions were the same, is there a technical reason the template would degrade to an unusable point?
Is there a rule of thumb about how long it can reasonably be expected to last?