This lateness is pretty common in partwork publications where you deal direct with the company.
I began collecting the Combat Tank Collection a few years ago and subscribed to company. I got sent my two magazines a month. Now the magazines actuallycame out every two weeks, and, since most months are longer than exactly 4 weeks, after a few months I was 5 or 6 issues behind the guys who were buying it from WHSmiths.
It's a poor poor show from GW but I gave up my WD subscription after 150 odd issues a good few years ago when WD became less of an "enjoyable read" and more of a "File next to the toilet in case of paper shortage" publication.