When your broadcast clip is missing the first part of the segment, it's sometimes possible to find that portion from the clip you already found. You can try the following:
1. Save the clip to your folder or account.
2. Scroll down the right-hand pane and click on the "Open Media Editor" button.
This will open the video clip in editor mode.
3. Check the timeline underneath the clip and see if the earlier portions of the segment can be found there. If it is, you can drag the timeline to the right to scroll to the earlier portions of the segment.
4. Drag the timeline to the start of the segment then, in the Editor tab, set the start time for your clip.
5. You can then drag the timeline forward (to the left) to quickly locate the end of the segment (if it's available). You can then set the end-point for the clip.