I have completed the transfer of the registrant for isaacbrocksociety.com and immediately used our new host’s free service to forward that domain to isaacbrocksociety.ca. As soon as this has propagated across the internet, no one will be able to get to the old wordpress site using the dot.com address. The transfer has been successful in redirecting to the correct page at the dot.ca site. So there is no need for authors to go through their old posts and change links. The only thing is that comments do not have the same permalink as before and it may be useful to change links to comments.
I personally have access to the old site (isaacbrocksociety.wordpress.com), if necessary. But at this point, I have trouble seeing why it would be necessary for anyone to access the old site.
(I’ve just checked, and it is clear that subscribers to the old blog do not need change their subscriptions to the new blog because the redirect takes them directly to the correct page).