There is a risk Mark that it has cross pollinated with any other variety growing nearby. say within a few hundred metres, since the tiny pollen grains can travel a long way in any wind.
You can have a harvest succession by sowing a late-maturing variety at the same time as Early Bird.
Or sow Early Bird 4 to 5 weeks later, even 6. Later sowings tend to catch up.
Then summer 2019 might be cold & wet and the late sowing will struggle to mature!!
