Also pretty sure none of them signed an LOI. However, signing an LOI does not start the clock. Enrolling in school full time starts the clock. Your last point makes sense since the LOI is only binding for one year if the plan is to greyshirt there is no reason to sign an LOI while still in HS.
Brooks signed his LOI this November. I haven’t seen that Lee, Beard or Nevills has of yet.
Starocci signed his letter this year as well