There will be a max of 10 of each app type listed per group for a total of 40 possible applications to post to (assuming 4 applications in a group) when querying $core_v2_group.ListNewPostLinks().
What version of the platform are you using? In 7.0, the plugins which define these links now expose configurable link counts in the control panel, defaulting to 10 per type.
This can be configured in the control through:
Control Panel > Site Administration > Site Configuration > Manage Plugins > Core Functionality Details > [ Wikis | Blogs | Forums | Media Galleries ] New Post Links > Configure
Hope this helps.