Germinating Sweet Cicely Seeds

In the past I've not had much success germinating Sweet Cicely (not seeds from Richters). I do realize this particular type of seed can be tricky. I recently purchased a couple of packages from you folks. Instruction are included. (Thank-you)
My question is:
The instructions do not specify which zones these apply to? I am in zone 5A. I assume sowing the flats as specified and over wintering outdoors will work in my zone as well. Or would you suggest I follow the alternative cold storage then sow directly outdoors in the spring.
Please clarify, I want to be extra careful this year.

The instructions apply for zones 7 or below, where winter temperatures fall enough to freeze the seedflats long enough.
In our experience, it is much better to sow in seedflats immediately after harvest in summer or early fall and put the flats outdoors under a mulch. We have never had as much success with spring sowing no matter how the seeds are stored. No doubt there is a protocol involving artificial cold treatment that will work as well as outdoor sowing, but we have not found one to date.