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The Banco Central del Ecuador was only a decade old when this series entered circulation — founded in 1927 under pressure from the Kemmerer Mission, the bank replaced a chaotic patchwork of private issuers that had plagued Ecuador's monetary system since the nineteenth century. The American Bank Note Company held the printing contract throughout this period, a relationship that gave Ecuadorian currency a consistency of technical quality that the earlier private-bank issues rarely achieved.

Pick 91 spans a full decade, meaning individual notes within the type can show considerable variation in serial prefix blocks and signature combinations — the signatures of the Gerente General and Comisario Fiscal changed multiple times across the 1940s.