The form control doesn`t support paging and thus only 50 forms will be presented this is a bug here is the bug in PITS, use the search functionality of the form widget.
If there is no search component into the form control the version of sitefinity running must be lower than sitefinity 6.0, please upgrade the site to version 6.0 for using the search feature of the form control.
Another way to manually set the form in the form widget is to edit form widget, click Advanced and in the textbox FormId enter the id the form that must be displayed. To get the Id of a particular form trough code refer to the API for working with forms.
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