The need and amount of assistance should have been spoken about during check-in. IF assistance was requested and acknowledged for the arrival part of the journey, there is somebody waiting at the aircraft door. Experience shows, that IF the assistance need is not visually obvious, the person needing the assistance needs to be pro-active to contact the assistance provider. The cabin crew can assist with that (or better: Should assist, since as long as the person is still in the airplane, s/he is the responsibility of the cabin crew).

The assistance need is registered in the PNR and as such available to all airline crew involved.

The printing on the boarding pass is optional. The cabin crew does get the assistance reported on their passenger log.

But, definitely, the person needing the assistance needs to be proactive.

If the assistance is late or not found or at the gate exit, stay in the airplane and the cabin crew has to solve the problem. Get out the airplane and you have to solve yourself, so to say.

If the person involved can not be pro-active him/herself, talk with the airline, if something similar to UM (Unaccompanied Minor) is possible. Additional instructions in the PNR might be the option.