Extended limitation for show cause notices must be invoked only where positive misdeclaration or fraud is established. Extended limitation provisions for show cause notices or lesser-charge demands must not be invoked without a positive misdeclaration or fraud; mere non-declaration is insufficient. If a long-established departmental practice is to be changed, do not normally issue notices beyond the regular limitation period, consider initiating the statutory notification procedure, and refrain from enforcing recoveries while notification requests are under Board or Government consideration.