As I have scoured Auction catalogues to put together a list of surviving 1870 $1 notes (amongst others) I came across an interesting find:
In the Torex auction of Oct 2004 an 1870 $1 note was listed as lot 7. It is serial number 326636/C.
In the upcoming TICF Auction, an 1870 $1 note is listed as lot 137. It is serial number 326636/B.
Both catalogues have pictures of the respective notes and the position letter is clear on both notes.
That must be pretty rare to have two notes from the same sheet surviving.