A few days ago, the Maine Secretary of State letter like this one to 5,830 voters who were enrolled Libertarians in late 2018 but who are not now enrolled Libertarians. The letter asks the recipient if he or she wishes to re-join the Libertarian Party. There is a postage-paid postcard inside the letter, to let the recipient re-enroll.
The Secretary of State will announce the results at the end of March.