I have just pulled a box of this very brand of duck eggs from my kitchen. There are no stamps on the eggs. The code on the carton is UK.1.666.L . This is not

I have just pulled a box of this very brand of duck eggs from my kitchen. There are no stamps on the eggs. The code on the carton is UK.1.666.L . This is not a Lion mark, and the code is not in the right format for a Lion egg. I don't know whether different schemes apply for duck eggs. The "1" is suggestive.