Data recovery isn't an exact science regarding it's retrieval. All that can be commented on for data recovery is that it's not a 100% guarantee success for any company. Sometimes it can be deleted. Other times it could be encrypted due to ransomware. But also it can be lost due to partition failure. And lastly there is mechanical failure. Three out of the four cases listed we have had to work with in the past. If there is mechanical failure, we recommend that the drive is sent out to specialists. Potentially with data being deleted and partition failures standard recovery software can be used to recover it. But with encrypted files due to ransomware, there are alternative means of accessing the data. Below explains a bit of what's involved with data recovery.
Recently we were tasked with the project of data recovery for a client that got hit with ransomware style of an attack. We were successful in the recent project but only because there was a hidden source of information on the computer itself. What isn't known to the normal everyday user is that if the system is allowed to run it's restore points regularly AND if they aren't corrupt for some reason then there is a decent chance to be able to access that data and recover it.
However the amount of information that is accessed is relative to the date that the restore point was made. But again this is under an assumption that the data was saved via system restore as we as the data being accessible in some form.
Alternatively the means of accessing the data on a hard drive can be done via recovery software. This software is used generally in any instance of needing to recovery data because of the way it looks for files. It will generally show the files that it can recognize, but the file names may not be present. However these scans aren't 100% guaranteed either.
If data sectors are overwritten then there is the likelihood that you won't get the data back. That goes for any types of data recovery. However in the case of what we were contracted for, we were able to recover 100% of the information needed. All data recovery jobs we do are fully explained before we do it because of the fact that the client needs to know what the chances of recovery are.