Thanks for the question (?)

There are 8 User memory locations for your custom Micro Tuning scales. These are stored with the User Bank and are available listed as “User”.
The User Bank is what becomes a Library. Each Library adds 8 additional Micro Tuning scales to your available scales (provided you have created and named them).

If you place eight User Micro Tuning scales in each of your eight Libraries, this will give you access to 64 + 8 (72) user created Micro Tunings.
Once you have done this, each Performance will have access to both the Factory Micro tunings plus the 64 you placed in your Library Micro Tuning locations, plus the 8 in the Current USER Bank.

User MicroTuning scales, 1-8, can be named (highly recommended). They are immediately stored when you configure them in slots 1-8.

If/When you store a Performance where a Part is is referencing a Micro Tuning location, it is that location #1-8 that is stored to the Performance. If you then initialize or change that location you will ruin the Tuning. It works just like the Factory locations... if you choose Equal Temperament, then the Performance points to Factory location #1... if Yamaha was to replace Factory location #1, then every Part that referenced it would change.

When you create a Library File from the current USER Bank, it adds those 8 Micro Tunings to your MONTAGE’s total number of available scales.

So, yes, you are wrong. You can have 72 in memory to choose from... any Performance can reference them.
Hope that helps.

Extra Credit:
The User Bank can contain:
User Performances (640)
User Arpeggios (256)
User Motion Sequences (256)
User Curves (32)
User Live Sets (8 Banks of 256)
User MicroTunings (8)
User Audition Phrases
User Waveforms

When you create a Library you do so by saving the User Bank as a “Library File” (.X7L)
When you then install the library by loading that File... you increase your MONTAGE’s access by the number of items you have written to ROM. All the Parts from all those Performances, all the Arps and Motion Sequences, all the Curves, and set listings (Live Sets), all the MicroTunings etc., are now accessible/available for use.

That is the advantage of the Library system... it’s all your custom data — and just like the Factory data, it’s always going to be there, ready to use.

Thanks mister bad mister.

I have a question - are we able to rename user microtunings? And will we every be able to apply them to the common performance?

I have a question - are we able to rename user microtunings? And will we every be able to apply them to the common performance

Yes, naming your MicroTunings is highly recommended.
Any of your 72 MicroTunings can be applied to any Part in any Performance.

My reference manual (release A0) page 82 shows

Tuning Name (Micro Tuning Name)
Determines the name of the selected User Micro Tuning. Touching the parameter calls up the input
character display.

[PERFORMANCE] -> [EDIT] -> Part selection -> ELEMENT/OPERATOR [COMMON] -> "Part Settings" -> "Pitch"
then "Edit User Tuning"
then touch "Tuning Name"