Rinse turkey parts. Transfer to 8-quart stockpot. Add carrots, celery, onion, bay leaf and water. Bring to a simmer. Cover. Cook at a gentle simmer for 2 hours or meat is falling off the bone. Remove cover last 15 minutes to reduce a bit. Cool. Strain. Transfer to container for refrigerator.
Next day: Fat will have risen to the top. Remove carefully and SAVE (freeze if using later)for making the gravy. Proceed with recipe or portion stock and freeze for later use.
To make the gravy on Thanksgiving: Drain pan drippings from the roasted turkey into a fat separator. Fat will float to the top. Do NOT discard. Pour pan drippings (without fat) into a measuring cup. Add turkey stock to total 4-5 cups. Set aside for finishing gravy.
In a 2-quart saucepan, melt the reserved fat. If you don't have enough fat, use butter to make up for it. Add flour. Cook for 1-2 minutes. Add turkey stock and pan drippings. Cook until thickened. Add more stock if needed...don't make it too thick!
Just before serving, add hard-boiled eggs (and giblets if you like) and cook until hot.