Not actually knowing which models came out when is still something that bothers me. It seems like we can group releases roughly around Adepticon (spring) and Gencon (summer) and then around November again (autumn). I'd like to make a chronological list... if anyone else wants to contribute, feel free, and I can keep updating this post. A combination of my memory and looking through https://www.facebook.com/arenarexgame/
has yielded this so far.
The beginning - Kickstarter. I assume that everything not mentioned below was part of the kickstarter, and seems to have been released to backers between 2013-2015. The post-kickstarter models seem to be...
Spring 2015 - Sulla, Stheno, Acerbus
Summer 2015 - Medusa
Autumn 2015 - Hagal
Spring 2016 - Khepros, Anum
Summer 2016 - Valen, Ywain, Hroka, Caho-Ta
Autumn 2016 - Dextarius
Spring 2017 - Leika
Summer 2017 - Tribune
Autumn 2017 - Iocasta
Spring 2018 - Cato, Atrox, Ladon
Summer 2018 -