re: Oops

My solution has been to glue on patches.

I would glue up a 2 part patch to form the miter joint. Pay attention to color and grain.
Then saw/file/sand the corner back to good wood.
Then saw/file/sand a flat surface on the patch.
The glue the patch on. Make sure you have extra patch wood on all sides. Use tape for clamping.
Saw/file/sand the extra patch material flush to the original frame.
Don't tell anyone about it.