'From Seed To Bloom' states:
Sowing
Indoors:- 6-8 weeks b4 planting out.
Outdoors:- Early Spring, when soil is cool and a light frost is still possible, or late autumn.
Depth: - Just cover
Germinating:- 14 - 42 days
Requirements:- Easy. 50F

Germania catalog states.
Solidago canadensis
Germination:- 5-8 days at 70F
Culture: - Indoors sow 8-10 weeks b4 planting out. Grow on at 55-60F.
Sow to Bloom:- 28-32 weeks

No need to stratify seed. Hope this info helps. If your 2yr old see has been in cold storage, it may germinate, if not, it'll be less viable.
Cheers Kim
Billabong Fresh Flower Farm