Mullard xf3 codes


I have come across Mullard EL34 xf3 coded tubes. They have a shield logo on top, a BVA logo, the legend "MADE IN GREAT BRITAIN" and codes xf3 and B 304 below which are, however, not etched into glass but printed in chalk ink. The sound is very good (smooth, uniform and detailed), but are they real Mullards?

Best regards,

If you go th the classifieds here on Audiogon and do a search on EL34 you will find some links. Follow them and you will even get reviews on that tube.
What do the xf3 and the B3O4 stand for?
If there is a hole in the guide pin then they are Mullards