The numbering in the catalogue was changed to accommodate the variety reported in the CPMS Newsletter, beginning with the 19th edition. PMG identified a DC-21g as DC-21f either because they were using an older catalogue, or, more likely, the note was slabbed before the numbering change occurred.
I agree that your note should be DC-21f.
The note shown in the Heritage link is DC-21g; their description is incorrect.