Your card was probably issued a number of years ago, because the new cards say on the back not to keep it with you. It simply shows that, over the years, we realized that we had to change our social insurance number protection practices, given the risk of identity theft when people kept it with them.
I cannot tell you how long ago the cards were changed. Recently, the 50th anniversary of the social insurance number was celebrated. As of this year, the social insurance number has existed for 50 years.