Uh-Oh, something @villagetinker didn't have a quick answer. I was hoping...
For those who have not seen an adjustable threshold,
this YouTube video gives you a quick answer about adjusting them.
My problem is that the middle 2 of the 4 adjustment screws are missing. I SHOULD have asked if someone has taken one of these things apart and knows if the screws can be replaced without having to rip out all the rest of the threshold assembly.
BTW, it is definitely not the sweep. The front of the house faces east and in the morning one can see a sliver of sunlight cast on the floor inside the door. It's definitely the threshold, probably caused when rolling in the "that's too small for Florida" gun safe.
As for other questions, the home is just over 2 years old and this is the one thing I missed putting on the warranty repair list. I have met the builder and might call him as @JohnN suggested.
That suggestion sparked another idea. Our purchase contract included an exhibit that lists details of virtually every thing used in construction, down to the types of bulbs used in light fixtures. Off to search that exhibit for door sills or thresholds ... which says "Eversill and Everframe" for exterior doors.
The question remains: has anyone had one of these things apart without having to remove the entire threshold?
THANKS to those who have already offered suggestions!