I have read that Springfield could not and did not retreat 1903's.
There is some evidence that Springfield Armory was retreating low-numbers rifles as late as 1925.
November, 1921 Arms & the Man Concerning the Strength of the Springfield by Hatcher. The new treatment started with guns numbered about 800,000, and when guns are repaired at Springfield Armory, receivers with numbers earlier than this are either scrapped or retreated.
February 1, 1925 American Rifleman Townsend Whelen answering question about heat treatment of 1903s. All rifles now being manufactured and all above No. 800,000 have the new heat treatment. Many of the older ones which have been returned to the Armory for repairs have been re-heat treated.
More about Sedgley:
The American Rifleman February, 1936 R.F. Sedgley, Inc. has offered to check the headspace of old-type M-1903 actions for NRA members free of charge. The firm is in a position to adjust defective actions and to proof-fire the rifle at their quotations. They are also prepared to re-heat treat such old-type receivers for added toughness or to eliminate the condition of excessive brittleness. Sedgley has so re-heat treated ten thousand or more of such actions and I have not heard of any blow ups to date.
