https://ecfr.io/Title-14/se14.3.121_1344
"§121.344 Digital flight data recorders for transport category airplanes.
(a) . . . The operational parameters required to be recorded by digital flight data recorders required by this section are as follows: . . .
. . . (19) Pitch trim surface position or parameters of paragraph (a)(82) of this section if currently recorded;
. . . (82) Cockpit trim control input position—pitch . . . "
So toss a coin. With help from Boeing and the carrier(s), the investigators should be able to determine the signal source.