Continuing with the "Fitting Dresses" booklet from the U.S. Department of Agriculture.
Neck line seam shows where flat collar is attached. This inside collar line may be longer than the neck line. This may be caused by failing to alter the collar after changing the neck line.
Rip the collar from the dress. Measure the dress neck line accurately from center back to center front, holding the edge of the measuring tape along the seam line. The stitching line of the collar should be twice this length. Take out the difference on each side of the center front of the collar. Pin the collar to the neck line and baste, easing the neck line slightly and holding the collar taut. Try on the dress again and be sure it is satisfactory before stitching.
Convertible collar stands away from the neck. The collar is too long for the dress neck line or the latter is too large.
Rip the collar from the dress. If the dress neck line fits correctly, measure it carefully along the stitching line. Then measure the inside collar length. If these measurements are not the same, take off the extra collar length at the ends. Pin the collar back in place and bast to the neck line. Try on the dress and see if the collar fits properly before stitching.
Straight collar rolls too high and rides the back of the neck. The inside collar line may be too straight or the neck line of the dress is too high at the back.
Rip the collar from the dress. If the neck line is much too high, trim it out slightly at the back. Otherwise, try basting the collar on with a seam deep enough to reduce the roll of the collar at the back. Or trim off the back of the collar. If this makes the collar too long, take deeper seams at the front.
Wrinkles where notched collar joins to facing. The facing may have been eased onto the collar or carelessly joined. Perhaps the curved edge of the facing was not clipped properly or the collar was too long.
Rip the collar from the facing up to the shoulder line. Make certain the neck edge of the facing has been clipped in several places almost the depth of the seam allowance. Repin and baste collar and facing together again. If the collar still does not fit smoothly, shorten it by taking deeper seams at the ends. Trim seams to their usual width
Have you had any of these issues with the collar on a dress or shirt?