yes, sometimes Joomla doesn't find updates although there are updates. I have a site, where Joomla don't find even its own updates.
You can manually install the update of BwPostman. To do so, You have to download the desired version from here: www.boldt-webservice.de/index.php/en/joo...n/101-bwpostman.html
, and install it manually like You install fresh extensions (at back end go to Extensions -> Manage -> Install).