Is my PSB too far advanced?

I have just planted out my purple sprouting broccoli and wonder if they've done rather too well so far. The best of them are about a foot high with 4 opened sets of true leaves with the next pair showing. They are very strong-looking plants with large leaves.

According to Dr Hessayon, they are ready for transplanting when 3" high, which should be between mid-May and mid-June, so are mine too advanced?

I am concerned they may run to seed.

I think with some of the newer varieties, you have in theory have PSB about 10 months of the year (if you believe the seed catalogues). Do you know what variety you have?

I have the early summer sprouting variety - planted a while ago and still only a few inches high in their beds but I assumed they will not harvest until NEXT summer...