Many years ago my dad gave me a subscription to a thing called The Seed Guild. The idea was that this guy had relationships with botanical gardens and arboreta around the world and had worked out an arrangement where he collected seeds from them and distributed them to Seed Guild members. I don’t remember the details but I do know the seeds for this lilac came from there. The catalogs I have (from the late 1990s) list three species, Syringa amurensis, S. josikaea, and S. wolfii, so I assume it’s one of those three. I’m leaning towards the last of them, which may more properly be known now as Syringa villosa subsp. wolfii (C.K.Schneid.). I had it growing in a container for many years and it never got very big. When we moved here in 2006 I planted it in the back garden and now it’s about 8 feet tall and obviously doing well.