Not-so-helpful advertising

Why is it that certain stores send out sale fliers without actual sale dates on them? I'm sitting here perusing one that came . . . oh, sometime within the last two months, and I have no idea if the sale's still on or not. Every single ad-item coupon in the flier reads: "Effective dates on back page".

What's on the back page? "Sale starts today and lasts 10 big days".

Well, gee. That's certainly helpful.....