I took mine to the dealer with the letter and service manager there said "Sorry - I see no problem with your rear window"
I had to agree with that, as I have no separation, so I asked about the wear spots in the fabric.
Reply there was " Why don't you cause some rear window separation, bring it back in a month and we will replace the top."

Haven't decided yet what to do ........

( I can probably cause separation by driving with top up and driver's window down - it sure does gyrate a lot in that situation above 60 MPH )