This is not an error, many of the Italian coins of this time had 2 different Roman numeral dates during the same gregorian year, so XVIII and XVII both existed in 1939.
There isn’t much difference in value between the magnetic and non-magnetic types, despite what some older catalogs say. There are of course rarer years, and rarer versions - magnetic or non-magnetic types of certain years.
The rarest might be worth £$€50 uncirculated, but you will never find it…. Keep looking though!
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