Joomla has ended 1.6 and 1.7 support definitely; you can't see 1.6 and 1.7 compatibility icons in JED.
We have followed the same strategy and we have not published Securitycheck and Securitycheck Pro 1.3.2 versions in those platforms
because we are developing new features and they have to be testing in the upcoming Joomla 3.x versions.
We have to do a lot of work!!