I'm not big into collecting my own country's coinage but the 67's I have in my collection have two different looks to them and I assume that is because of the difference in the silver content. Other's disagree and say there is no way to tell. The "silver" ones I have look like silver coins and the other's look more like nickel.
I asked this question a long time ago, because I had a couple rolls of 1967 Canadian dimes. I didn't really get any definitive answers. Luckily I realized later that my rolls were actually of 1964 Canadian Dimes. Problem solved. 80%