Whether a seed needs cold stratification or not does not depend on the cold tolerance of the species. Alpine plant species naturally grow in the very cold, above the tree line on mountain tops or sub-arctic. At least half of them require no cold treatment before seed germination, and often germinate better without a cold treatment.
I don't think there is anyone more qualified than Ian Young to advise on Erythronium. As you have probably already discovered, different Erythronium species' seed from different parts of the world react differently to storage and germination. Ian's advice is scattered throughout the SRGC forum, but culminates with his online book, which he graciously publishes on the SRGC forum as he completes the chapters. The chapter on seed (2015) is in his Bulb Log here:
http://www.srgc.org.uk/logs/lo...
I haven't had much success to report with my attempts at germination back in 2010 and 2012. But I have to admit that I only tried the standard variations of seed treatments, and didn't have Ian's advice to refer to.
