I seem to remember the reason that the peanut-free symbol was added to the snack size bars was because most primary schools have peanut bans. For example, peanuts are banned in my daughter's school and during lunch time, anything with peanuts or a may contain peanuts alert is not permitted in the classroom or school. Having the peanut-free logo on the bar ensures it is safe for child to eat in the classroom / school during lunch.
I just called Nestle Canada. They confirmed that if a chocolate bar is manufactured in a facility that uses peanuts or tree nuts, an allergy alert will always be added to the packaging. She told me if there is no allergy warning, the product is made in a peanut-free / tree-nut free facility.
She also mentioned that there are regular size Kit Kat, Smarties, etc products made in other countries (ie: Europe, United States) that do have a peanut allergy warning on them which could be found in specialty shops, so she said to always read labels to ensure the product is safe. There are also Kit Kat/Smarties/etc products made in Canada in facilities that use peanuts (ie: Kit Kat Bites, Smarties Easter Eggs, Smarties Christmas Tree Ornaments, etc) which have a peanut allergy alert. So always read labels.
So in summary:
If a Nestle Canada chocolate bar is manufactured in a facility that uses peanuts / nuts, an allergy alert will always be added to the packaging.
So we will continue to eat Aero, Coffee Crisp, Smarties, Kit Kat and Mirage - and always read the labels as well
p.s. and yes Jessica: some products have a peanut-free logo, but at least 90% or more of the food I eat does not have a peanut free logo - bread, cereals, milk, juice, chicken, soups, etc don't have the logo but I still eat them anyway