If there is validity or expiry for every currency same as day to day life needs, then people will make use of it and exchange to new currencies at the right time. This way everything can be made to be in circulation rather than getting accumulated for years. Here black money can also be avoided.
How can everything be in circulation? You just change old paper with new paper, that's all, it has nothing to do with the circulation. If we think about something like spend your money or it will expire, then it's a terrible idea because with that law, investors won't exist (you have to collect money before investing in something).
I tend to agree, just might replacing the physical money with a new one or phasing out the old design and must put a new one. That isn't an expiry date of a currency, because if any currency that has an expiry date will become unacceptable to the community, what if they store old currency and they forget to exchange it with the new one. It seems the same here in our country, but people still can exchange their old currency directly to the bank with the same amount.
And I think, that isn't a perfect way to combat black money, individually can use the currency without knowing by the bank or any financial institution that declaring the transfer of fund.