20 Francs

This note ran through an unusually long issuance window — over fourteen years and multiple signature combinations — which reflects the Belgian National Bank's conservative approach to note replacement rather than any monetary instability. The Stacquet & Franck pairing covers the bulk of surviving examples from the early-to-mid 1930s, while the 1940 Sontag & Janssen dates correspond to the months immediately surrounding the German invasion of May that year.

The "TRÈSORERIE"/"THESAURIE" overprinted variant (P-111) was a wartime administrative reclassification, shifting liability from the central bank to the Treasury — a distinction that mattered considerably under occupation.