504ZXX was a youth model of the zippered version of the 501XX, specifically 27 to 29 inch zippered version with the part number 504Z. 501ZXX, the zippered version of 501XX, is said to have been born in 1954, while 504ZXX has been in production since 1952. This one has a leather patch, but the red tab is a "double-sided tab" with embroidery on both sides, and the guarantee ticket is made of paper and is "for over 85 years", so it was probably made around 1957 (generally, the transition from leather to paper patches is said to have taken place around 1955, but this transition did not take place all at once, and the leather patches that remained at each factory may have continued to be used after 1955). . There is no denying the possibility that the leather patch on this one is newer than 504ZXX with a paper patch.
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