There are also other credible books that refer to the seal.
Please see the following:
This book is credible in chinese, but as if the translator did not understand the history fully, so I edited his translation:
A treasure handed down from ancient time, cited from "An Introduction To Ancient Seal" by (Luo Fu Yi). The original explanation stated: "The copper seal (Yi Guan Bei He Tong) in Standard Script, a treasure handed down from the ancient time, was used to stamp at the back of (Hui Zi, a kind of paper money in southern Song Dynasty, 1127 A.D. -- 1279 A.D.). According to (Song History -- Carriage and Clothing Etiquette Record): "The Ministers again said: 'The affairs of official seal is important, when there are official seals which the seal characters become blurred through long time of using, that should be recast, unless ask for imperial decree, it can not be recast.' When it was recast... (The Hui Zi Affairs Office Under Tea Monopolization Site in capital) would give 25 seals for each (Jie, which means time limit of circulation):...there were 12 (He Tong Yin, which means He Tong seal), among which are 2 seals that had the characters (Yi Guan Wen, which means 1000 Wen), each was cast with characters (Hui Zi Ku Yi Guan Wen He Tong Yin, which means Yi Guan Wen He Tong Seal of HuiZi Treasury)." So Paper money of Song Dynasty have He Tong seal mark. But there were many kinds of paper money at that time, it is not clear which kind of paper money this seal was applied.
Just as I said before, the characters on the seal are Song Style Characters, In fact, they were at first called Qin Style characters in Southern Song Dynasty(1127 A.D. -- 1279 A.D.). The original words from (Luo Fu Yi) is not full, and (Wang Guo Wei) only told us that the seal of (Yi Guan Bei He Tong) was used for paper money of Southern Song Dynasty(1127 A.D. -- 1279 A.D.), he did not tell us what the characters' style was. In fact, it can be concluded as a Song Dynasty(960 A.D. -- 1279 A.D.) seal, but it is hard to judge that it was from Southern Song Dynasty (1127 A.D. -- 1279 A.D.) without recognition of the characters' style on the seal.
I will show some details on what is Song Style Character, its origin and relation with Qin Style Character. Qin Style, a style we seldom or never heard before. I will then analyze why the seal of (Yi Guan Bei He Tong) was from Southern Song Dynasty(1127 A.D. -- 1279 A.D.), and why it and the relevant paper money are so scarce nowadays. I will show that later!