Let me run that by you again. Although you may set your blog to display 12 posts on the front page that has nothing whatsoever to do with the number of title links the widgets will display in the sidebar in "top posts", "recent posts" or in "recent comments".
As all data in sidebars is cached, the top posts, most recent posts, and the most recent comments are not displayed immediately. There is a time lag before they appear.
However, setting that aside, the sidebar widgets are hard coded to display the maximum number of 10 (ten) "Top Posts". And the maximum number of 5 (five) posts for both the "Recent Posts" the and "Recent Comments" widgets. You cannot change this. So if you used to have more than the maximum numbers I gave you above displayed and don't now then there was a problem that staff corrected.