National Do Not Call List has been in the USA for a long time
It has only been in Canada for about 10-15 years.
Most companies that do outbound calling to the general public buy numbers lists.
Their provider must comply with DO NOT CALL requests as a company can be fined otherwise.
Market Research firms change the last digit to make it more “random”.
DO NOT CALL (DNC) doesn’t apply to legitimate surveys, political campaigns & charity fundraising.
You can however ask to be put on their company Do Not Call list.
This way you won’t get another call for another least 6 months to 1 year.
With market research different number lists are loaded for each survey.
That means that while chances are slimmer; you may get called again.