Johnnie walker blenders batch serie

KrizL

Can anyone help me with the blenders batch serie. It's really confusing to me. 

red rye finish no. 1
bourbon & rye finish no. 2
triple grain american oak no. 3

directors edition major peat no. 5

directors edition the bacchus No. 6
wine cask blend exp. 6
sherry cask finish exp. 7
rum cask finish exp. 8
espresso roast exp. 9

Why is there a no. 6 and a exp. 6? 

And what is the difference between no. And exp.?

Why isn't there a no. 4?

Thank you