Good one! The only regulation is that here in Canada they are 'encouraged' to use the wording 'may contain' instead of the other variations of such statements. I wonder if we can start a petition to make 'may contains' mandatory for shared lines. (Shared facilities would be even better, but I know many people are ok with shared facilities.). With such a strong food allergy community, we may get enough signatures.
But then again, many - and I would confidently say most - people still believe that no may contains statement means it is safe. Their tolerance levels may be higher, their comfort zone bigger, etc. But I truly think most of them do it because they either aren't educated of the risk or simply don't have the time and energy required to call/email for each and every item and choose to accept that risk- or the stigma of being an allergy person/parent and needing to know these 'ridiculous' details - when half of time the answers aren't clear anyway.
And then restaurants cooking for people with allergies rarely, if ever, know anything beyond what is on the label! (I had one restaurant refuse to serve me an item because the chef couldn't call and ask about may contains because it was after hours - bless that Disney chef - but most wouldn't have a clue.). And people wonder why I won't eat out anywhere... I cannot trust them to know as much as I need them to know about the ingredients they are using.
And the ongoing world-wide cumin/spices contamination, with products still accepted to be on the shelves without a warning...
The situation is extremely complicated. Preaching to the choir here, possibly even the pastor, I know. LOL.