Mystery surrounding Amsterdam stamp

Some time ago, I found an envelope from 1947 originating from The American Express Company in Amsterdam and addressed to the same company in New York. The envelope was franked with a 1 guilder stamp, a 50 cent stamp, and a 22 cent stamp. In 1947, the measures taken to combat foreign currency smuggling were still in force. Hence the red stamp impression: Offered sealed for dispatch pursuant to exemption No. 341. Apparently, The American Express Company had an exemption from the Ministry of Finance. That alone made the envelope collectible. What did not immediately stand out was the strange Amsterdam stamp. However, upon close examination, it turned out that the name AMSTERDAM in this stamp was 'out of alignment'. The stamp was of the type manufactured by the Amsterdam stamp factory Posthumus. A beautiful impression had been applied to the back of the envelope. However, the AMSTERDAM 1 stamps that I did find in the stamp books were manufactured by Martin in Berlin and De Munt in Utrecht. The one by Martin originally had hatching that was later removed by De Munt. This stamp did not resemble that of Martin. The stamp model was also smaller in diameter. The stamp was rejected and destroyed in 1912. The Mint's stamp had Roman month numerals instead of Arabic month numerals and so-called 12-hour characters. The impression of the AMSTERDAM 1 stamp on the envelope had Arabic month numerals and 24-hour characters! What was going on here? I found the answer in the stamps that were in use at a few branch post offices in Amsterdam. Initially, the branch offices did not have a street name on the stamp, but a number. Only a few branch offices received a long bar stamp with the branch office number. Branch office number 2 was Amstel. This office possessed four stamps with the branch office number. However, according to the note in the stamp book, stamp number 1 was replaced in September 1926 and destroyed in October 1926. The branch office on the Handelskade also had a stamp with the branch office number. This branch office had number 4, which was indicated in the stamp after AMSTERDAM and serial number 1. The branch office was closed on July 31, 1911. What happened to the stamp? No note can be found in the stamp book. Therefore, I conclude that the numeral 4 was removed from the stamp and that the hour characters were replaced. The stamp was put back into use, but when? I have only seen impressions from 1947 and 1949. Was the stamp only used for stamping letters that went through currency control? That is quite possible! These letters went abroad. And that is why not so many of them can be found. It was a nice riddle, but with some searching, I eventually arrived at the solution.