I've just looked at my A500 (circa 89) and the serial no label is in a slightly different font type.
All info is the same EXCEPT that my A500 is 5v DC 2.5A, not 4.5A.
Also, there is a second barcode label positioned above the serial no label. The number is very short in that it matches the serial number! No other info appears on this label.
The actual serial number font is nothing like yours. The type is the same as you see at the bottom of bank cheques, and it's been printed after the label. Yours does not ring true.
Hmm. Is the serial number plate somekind of scam or false? It _could_ be counterfeited, but can't see any reason for anyone to do it and sell it to flea market. Strange, anyway.
What are other serial numbers? It would be nice to see a few for a reference (from matching year, perhaps).