Hi Sam, I've been looking at this and it just goes to show that there is so much variation on information not only when to sow seeds but how the plants are described.
For example snapdragons/Antirrhinum are described here as perennials but many would say that they are either half hardy perennials or even annuals. Another example would be Aubrieta which many packets say to sow in Feb rather than March
. I'm giving some of them ago in Jan,just to see what happens. I'll sow some more later on as well.
I treat all the information as a guide and adapt it to my own local climate, growing on conditions and experience