Doing some more digging, I stand corrected on there not being any conversions. In 1895 and 1901, rifles were converted to cadet rifles, 1800 in the former year, and 7000 later. It is not clear whether the 7000 figure includes the 1800. The conversion, however, involved removal of the sling swivels, re-finishing the barrel and stamping new inspectors cartouches with the conversion/re-issue date, sometimes with the old cartouches still fully or partially visible.
The idea that Springfield installed sling swivels on surplus Cadet rifles may be true, but I can't find much to support it. One report says that for the years 1867 to 1886, only about 30 cadet rifles were sold by Springfield to "officers and civilians" which would seem to include non-government military academies. On the other hand, sale of cadet rifles made up by various companies from condemned or surplus parts was so common that officers at Springfield regularly deplored it. Of course, they could have stopped it by scrapping parts rather than selling them, but the sales brought in badly needed money. (Oh, that our military today were so concerned about saving money!)
Jim
Jim