I have heard of this .. an yes thread does age but it takes quite a bit of time , but the break test will tell you if its not suitable .
I agree with other postings that many classes have become a new format for selling. I recently attended one and was shocked at how many special "tools" they told each student were needed. I found it bordered on unethical since they were already paying big bucks for the class. It made me question any info given in the shop .. as to the motives.
But then again so have some of the magazines... it never fails one of the quilt patterns in a magazine requires a specific tool or ruler , and no alternate method without the special tool is given.