I went on the "National Archives soldier and sailor website" and typed in the last name "Pennell". Over 150 names showed up but one caught my eye, the only "Pennell" that was a Lieutenant. From what I have read, this may or may not be the same Lieutenant that carried the brigade guidon, if so this would be the "Guidon Marked 2". Now the 19th USCT was in the Second Brigade. So I believe that is the guidon/flag in question.

Christopher Pennell (First_Last)
Regiment Name 19 U.S. Col'd. Infantry
Side Union
Company I
Soldier's Rank_In 2" Lt.
Soldier's Rank_Out 2" Lt.
Alternate Name
Notes
Film Number M589 roll 67

I will track down the Six missing flags and read more books on the Crater and report back my findings.

Have a good morning,

Shawn Prouty