The best time for distribution of forged new currency is ALWAYS the first time this new currency is launched, usually bankers are aware of new security features for the new series, and others are not.
Early stages of launching new currency involves people in a rush to try / feel the new banknotes, that’s when counterfeiters Hit and take advantage. Despite all awareness campaigns by government some people get excited with the new colors more than noticing the absence of security features (it happened with the 1996 series).
It is just a stage of launching a new currency and law enforcement should anticipate that in advance, so it comes as No surprise!