Copying TM machine backup from external usb drive to system one

[Mac2013orlater]

OS X 10.9.5 on iMac 2013 late. No Bootcamp. OS X a originally installed by factory plus all those updates till 10.9.5.
One of our Time Machine destinations is an external USB drive, a HDD, not a SSD.
Recently drive generates additionally to its typical noises some new noises nor typical for a hard drive.
So it is going to raise a RMA on provider and be sent back for replacement or fix.

All these backups generated by Time Machine need to be backed up on some other container before
the drive leaves our house. We tried to use iMac system disk / volume. Once as normal user, another time as administrator. Every time the result of the copy counts much less items and GB's of size than the original on that external usb drive. Instructions found on pondini.org were followed.
How to be sure all of TM backup on external usb drive was copied to iMac internal system volume?

Mac OS Journaled partition, case non-sensitive on GPT formatted external usb drive.

 

[Mac2013orlater]

Additional attempt to generate a copy of TM backup was made (TM backup original on USB external drive, the copy on OS X system volume) one day later. Two users made that retry: admin and non-admin. Results are more satisfying, at least if it comes to the copy made by admin >> the copy is identical as the original regarding the number of included items, and quite identical regarding the overall size (905 Bytes of difference). For some reason the Finder was not able to achieve this one day earlier.
The copy made by non-admin user still shows significant discrepancies against the TM original backup. These are discrepancies regarding the number of included items (403 019 in the copy vs. 981 369 the original) and the overall size (43.72GB the copy vs. 108.99GB the original).

Unfortunately severe problems arise if to move the copy back to USB external drive. The data is moved by administrator.
The process aborts with an error message something like "not possible to copy because you do not have sufficient access permissions to some items", then the message showing error number -8003.

Is this a sign that the TM backup original was not fine?
Or something ran wrong during the copy or copy-back to usb?

Instructions found on pondini.org were applied while making the copy of original to system startup drive.

 

[Mac2013orlater]

It turns out that admin had just read-only access to the copy of TM backup.
After assign of read/write access it works much better.
However one point still unclear.
According to Finder the copy of TM backup features nearly 870 000 items.
The restore operation, move the backup copy back to usb external drive, its preparation stage
find nearly 1 000 000 items.
Where this discrepancy from?

 

[Mac2013orlater]

I figure out that due to hard links used for TM full backups might be not optimal to do a copy
of TM backup manually using copy&paste and Finder. The copies addressed in this thread were made
even that way.
However according to pondini it is possible to have a copy using Finder.
So I am unsure which is the proper point.

It is a my current concern because after had copied from TM backup copy to TM backup destination volume
the remaining space is smaller the prior the whole mission with about 70GB.
I do not expect such big jump in backup size on one backup run after the mission completed.
Any idea regarding possible reasons and fixes?

For your convenience the mission was to have the TM backup temporarily on some other volume
then the original TM backup destination, make some maintenance of TM backup original volume,
have the TM backup back onto its regular destination volume.

Fortunately, it is one of rotating backups and non-critical to have lost the backup depth it provides.
So I decided to start the backup on this drive from the scratch. Next time the copy of TM backup made on other volume/drive will be needed, it will produced not by using Finder << that's the lesson learned.