Jim,
See 4 scans below: two 1908 Sullivans, one 1909 Johnson, and one 1915 Carpentier. While it appears that there is a cream Sullivan and a white Sullivan, I think it's just aging, as I have several other 1908s and the back toning varies from white to cream, depending upon aging, I guess. Also, you will notice that the backs of the 1908 and 1909 are slightly different. The 1915 is written in green. Hope this helps.
1908 Sullivan
Another 1908 Sullivan
1909 Johnson
1915 Carpentier