Remember - probably MANY, MANY of the employees you are dealing with over the next eight weeks are new, (barely trained), temporary/seasonal employees...
My JoAnn's is very good generally with the coupons. As long as the coupons are from different sources (example: one from weekly newspaper, one from mailer, one from in-store handout), I have had no problem using multiple 40 or 50% off coupons, as well as the "total % off" coupons. In fact, I have also been able to use Michael's coupons in the same transaction on items Michael's carries, of course.
Be polite - it goes a long way - and remember that many of these employees have little or no experience!!