There is nothing contractual that would prevent you from JS'ing in for duty periods that exceed 13.5 hours from your JS show.

There is a contractual provision that indicates you will not be subject to discipline if your JS doesn't make it to Memphis if you meet the wickets, but that provision goes away should the FAA ever determine the JS is part of your duty day.

When it suits Mgt, and they become aware of it, they have removed people (sporadically) from trips where the no harm\no foul provisions aren't met. And pondered at how could someone be rested to operate the 777 to Narita.
Well, long ago the company taught me that I was better rested sleeping in my own bed. And long ago, company taught me that the Capt and Crew should come up with a rest plan for the longer duty periods-especially those with RFOs.

So, doesn't it make sense for someone to Plan to rest shortly after TakeOff--then come back on duty 3 or 4 hours later?