Can you draw the line to help me determine what edits made to Parts in Performance Mode will be saved on power off OR will be lost meaning they will need to be saved in an AUTOLOAD file?

First, let’s clarify these two terms concerning the Motif ES

STORE - is the act of pressing the dedicated [STORE] button and writing data to the internal User Memory
SAVE - is the act of pressing the dedicated [FILE] button and writing data to an external storage device (SmartMedia or USB)

Only [STORED] data gets SAVED.
Only data properly stored to internal memory get written into your File.
In the upper corner of the Motif ES screen a small, inverse video “E” appears anytime a program has been Edited but not yet STORED.

In your quote above I’m sure you meant to say “STORE”
Here is the line I would draw:
All edits made to Voices, to Parts of a Performance, to Parts of a Mixing, to the Song sequence, to the Pattern Sequence, to the Master mode, to your Utility settings — all will be Stored to internal memory. You press the [STORE] button when you complete editing and before you move away— store your Voice edits before you move away, store your Performance edits before you move away, store you changes to the Sequencer before you move away... etc., etc...

When you edit and press [STORE] all the parameters are stored to internal memory... and they will survive power down and power up. The only data that does not survive power cycling are the Audio Samples on your expansion DIMMs and the RAM Banks on your three PLG Boards (36/02 AN Board, 33/02 VL Board, and 35/00 DX Board). Again these would be custom “from scratch” sounds made with the “AN Expert Editor”, the “VL Expert Editor”, or the “DX Simulator”, respectively).

This content must be reloaded each and every time you power up. This was how data management was 18 years ago when the Motif ES came out.
Starting in 2010 Yamaha introduced built-in Flash memory which maintained Audio Samples between power cycles.
PLG Boards were gone by 2010...

The RAM Banks on your three PLG150-series Synth Boards behave just like volatile memory of your DIMMs... the data must be restored from a File each time the instrument is power cycled.

Ok, then please check my understanding on two points;
1) whatever edits I make to internal preset voices or internal user voices that are attached to any parts of my performance can be stored and will then be preserved in my internal memory on power off.
2) whatever edits I make to PLG user voices that I create starting from PLG presets, NOT by starting from scratch with expert editors, may likewise be stored and then preserved in my internal memory?

1) whatever edits I make to internal preset voices or internal user voices that are attached to any parts of my performance can be stored and will then be preserved in my internal memory on power off.

True if you add “to my internal User Bank”

Whatever edits I make to internal Preset Voices or internal User Voices that are attached to any Parts of my Performance can be stored “to my internal User Bank” and will then be preserved in my internal memory on power off.

2) whatever edits I make to PLG user voices that I create starting from PLG presets, NOT by starting from scratch with expert editors, may likewise be stored and then preserved in my internal memory?

True if you add “or PLG User”

Whatever edits I make to PLG User Voices that I create starting from PLG Presets “or PLG User”, NOT by starting from scratch with Expert Editors, may likewise be stored and then preserved in my internal memory

Got it. thank you again Phil....