Yes, there was an email for the early bird special when MC24 was announced. The problem though was that some email providers blocked the emails, thus they failed to deliver the emails to some users (I think it was Microsoft?). Anyways, if you didn't receive any emails check your junk/spam folder, otherwise it's likely your email provider simply blocked the emails from coming through.
To compensate for this JRiver did enable a feature in older versions where when MC checked for updates, it'd display a message in the action window area about the upgrade being available. Of course, if you disabled automatic updates, you wouldn't of seen this message.
If emails fail, I'd recommend checking the forums at least once a month because any early bird specials of new MC versions will be announced at the top of the forum section.