The tags for my lavender blue away and I have spent hours trying to figure out what it is so I can buy more. Many die in my zone in Massachusetts. They were evergreen throughout the winter, whereas others had die back. The leaves are grayish-green and longer than other lavender (Pictured first) than the lavender with growth coming from the ground (Second two photos).

If I had to guess it is either Hidcote, Phenomenal, Munstead, Grosso, or Elegance.