Restore from Time Machine from Server

I maintain some 10 computers for my family and my business. Yesterday I tried to upgrade my business partners mac MINI 2014 from Yosemite to El Capitan.

I had already done it with two MacBooks and everything seemed to work.

This machine must have had a Catalog Error on its hard disk. So.. the installer would not install.. it would check the HD and then say.. reboot and make you choose another disk since it no longer would even start into the old system. So the Harddisk of my business partner was defect, thank good we had this machine make backups onto our Server, running the most recent Server software by apple and giving Time Machine capabilities to all our users.

I made a usb reinstall drive, erased the faulty HD, installed El Capitan.. and was asked where from I would like to restore.. I logged onto our internal network.. and.. did NOT find a way to connect to the Time Machine Backups.

I tried it ten times with Migration Assistant... I would not see the Server.. it says.. error accessing the miniserver.local/Backups ...

You cannot restore a machine if you do no longer have access to the machine! So it seems to me...

I tried everything over the network, I even unhooked the hd which contains the TM Backups on the server from the server (the Migration Assistant would only see the backup of the Server..not of the clients which made backups on the server).

I copied the backup mini_3.sparsebundle to another disk.. I can access it.. but it does not contain Users..only machine, network and application data.

Anyway.. What a mess.

I do not know IF I did something wrong.. But thank good that I did not really rely on this Time Machine Technology...It was no real important data and all our business Data is on the server and in the cloud.. But... what an unexpected result... I mean... what is Time Machine on the Server Backups for if you cannot easily restore the whole machine after a HD failure... ?

Any suggestions?

Pierre