An interesting old
collection, from which I too acquired a couple of coins.
Heynen's too was an interesting old
German collection, but I think you're unlikely to find your coin in the
Heynen catalogue of 1976, because that was the
collection that
Heynen, who died in 1970, donated to a
German museum.
Heynen was a friend of Reusing's, and at an earlier date
had evidently sold or exchanged or given a substantial number of coins to Reusing, which are now coming back onto the market via the coin dealer
Olding.