in HDD manufacturers' manuals or any review showing how many months or years without use an HDD can remain stored without power supply and this does not harm damage fails the mechanics, lubrication and engine of the HDD?

What's stopping you from checking HDD manufacturer manuals?

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Joep - http://www.disktuna.com - video & photo repair & recovery service

I saw several manuals and didn't find any, maybe some have this information

At best they could include statements on drives with identical bearings / lubrication. Any new model for which a manual is written can't have this tested because none of the drives aged enough.

If you doubt long term HDD storage then you should not rely on it.

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Joep - http://www.disktuna.com - video & photo repair & recovery service