Yes, the originals in the media bins are always complete.
That said, if you have trimmed one - from a bin and not the timeline - it will reflect that trim. Files in a bin can be copied, each individually trimmed, then dragged to the timeline where only the area that hasn't been trimmed out will appear. Or use the ADD button below the preview window. Click its chevron to see the options.
Of course, trimming by dragging borders of a clip, or splitting and deleting portions, can be handled on the timeline.
Check this out.