Why Did India...

Get Some Coins minted at Foreign Mints?

For example, 1988 50 Paisa in Canadian mint.

N#1606

Those are numbers from Krauze. Based on timing Indian mints were probably still busy minting cupro nickel coins or converting to presses that can handle steel coins.

We do not have insights on the way government officials thought four decades ago.

The domestic minting capacity was likely insufficient to meet sudden spikes in demand in some years.

That makes good business sense (even though governments often don't act like businesses).

It allows you to avoid the expense of installing “excess” minting capacity.