1955-S RPM #4 Cross-Reference research
In the process of attributing some varieties I found in a recent lot of 1955-S BU Rolls, I realized that the many RPM #4 die stages had some un-connected cross-references. It took a bit of study of all my RPM #4 and related BIEs, and checking online for Cuds, but ultimately I have found linkages that I don't think were previously known:
The series of BIEs listed in Cohen from BA165...BA169 are actually stages of RPM #4. Cohen only recognized the S/S/S RPM #1, so was not focused on the mintmark when she listed these Associated BIEs. These BIEs roughly correspond to RPM #4 Stages D, E, F, G which are starting to show BIE die cracks and depressions prior to becoming a full BIE.
Cohen noted that more research was needed to determine if BA140 was an earlier stage of BA143. I have done the research and can confirm BA140 is indeed roughly equivalent to RPM #4 Stage I/J. Cohen's description is broad enough to encompass both stages in that the distinguishing feature is a die crack that becomes a retained cud, further listed as RCD-1C-1955S-01R on COC.
The remaining cross-reference revelations are best seen in the table below. Note that the ultimate stage of this RPM used to be known as Stage "K" but is now known as Stage "L" on VV as a new stage was added. I was not aware of this and now need to go back to re-label my examples. This BIE is known as the "Sausage" BIE and is the largest BIE in the Lincoln Series.
Here is a table I created showing the cross-references: