Personally, I think that the chances of ever getting a ricochet inside of your glasses and then into your eyes is pretty much non existent. But there is that chance.
There is a far greater danger, however, in driving anywhere we go or riding a bike somewhere, even going up and down stairs and potentially falling. The chances of one of those things critically injuring me is far greater, in my opinion and experience (not me obviously, but others I know) than the risk of a BB finding it's way into my glasses from a small slit and then ricocheting into my eye in such a way it will cause lasting damage.
The moral of the story, we all take risks, most of the time we don't think about it. We could all be safer, but we do drive that 10mph over the speed limit, or do any number of things. I really don't think that full seal vs. nearly full seal should be a big concern, and if it is then I would imagine we are choosing the wrong battles to fight when it comes to safety.