That is one other disadvantage to free matter.  It is usually not traceable. 
But I didn't know you could insure free matter mailings.

At the risk of opening another can of worms, does anyone remember 2 for 1 
bus travel where you sent to AFB for a book of 2 for one coupons and when 
you purchased a ticket a companion could ride free to help you?  That was 
another thing that was flagrantly abused by the blind.  Most blind people 
used it among themselves to get tickets for half price between the two 
people riding.  As a result, I don't think it is available any more.  Of 
course Greyhound has drastically cut back its service, but that was another 
privilege that was blatantly abused by the blind.

One bus driver I knew of actually tried to do the right thing.  There were 
two people riding 2 for one, but the helper wasn't helping and the driver 
was doing all the helping.  So he told him to either help him or go buy a 
ticket that the 2 for one was not a free ride.
Harvey