According the the Fjestad Blue Book, the last BDAs were made in 1997. Maybe you encountered new old stock? It happens.
This might be older stock but not that old. The last run was in 2009 IIRC. $600 us a fair price for a NIB example. I personally like the Beretta version better. I had one but sold it a year ago. I sold it for $500 with 2 10 rounders and 2 Mecgar 13s. It was nickel in excellent condition.
$600 is a fair price not a steal IMHO.
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