Hours of searching through datasheets later, I think I've identified them. They're all transistors (SOT-723 package).
"42" marking = DTC043ZMT2L
"XK" marking = RN1110MFV
There are some others on the joy-con boards marked "49" and "69".
"49" marking = DTC043TMT2L
"69" marking = DTC024XMT2L...