In files identified as containing corrupted blocks punch holes in the valid blocks so they don't take up as much space

_punchHoles.ps1

$blockSize = 4KB
$buffer=[byte[]]::new($blockSize)

Get-ChildItem -File `
| Sort-Object -Property Length
| %{
	"$($_.Name)`t$($_.Length / 1MB -bor 0)MB"
	$path = $_.FullName
#useful if your files are patchable eg torrent-sourced
sudo cp --reflink=always $path "${path}_rescued"
	chmod u+r $path
	$file = [System.IO.File]::OpenRead($path)
	chmod u-r $path
	
	$current = $NULL
	$read = $NULL
	$occupied = 0
	$bad = 0
	while ($file.CanRead) {
		$position = $file.Position
		if ($position -and !($position % 256MB)) {
			"`t$($position / 1MB)MB"
		}
		
		try {
			$read = $file.Read($buffer, 0, $blockSize)
			$current = $True

			if ($read -lt $blockSize) {
				$file.Close()
				$current = $False
				$position += $read
			}
		}
		catch {
			$current = $False
			++$bad
			$file.Seek($blockSize, 1) | Out-Null
sudo fallocate -p -o $position -l $blockSize "${path}_rescued"
		}
		
		if ($occupied -lt 0) {
			if ($current) {
				$occupied = $position
			}
		}
		elseif (!$current) {
			if ($current = $position - $occupied) {
				"`tPunching $($current / 1KB -bor 0)KB"
				sudo fallocate -p -o $occupied -l $current $path
			}
			$occupied = -1
		}
	}
	"`t$bad bad ${blockSize}B blocks of $($_.Length / $blockSize -bor 0)`n"
}

diff.ps1

#!/usr/bin/pwsh

Filter Output { Param($colour)
	$num = ($_ -split '(?<=^[a-f0-9]+:\s)')[0]
	$num | Write-Host -NoNewline
	$_ = $_ -replace "^$num",'' -split '  (?=.{10}$)'
#	$_[0] | Write-Host -NoNewline -ForegroundColor $colour
#	'  ' | Write-Host -NoNewline
#	$_[1].PadRight(10, ' ') | Write-Host -NoNewline -BackgroundColor $colour
(
	[char]27,
	'[',
	(31,32)[$colour -eq 'Green'],
	'm',
	$_[0],
	[char]27,
	'[39m',
	'  ',
	[char]27,
	'[',
	(41,42)[$colour -eq 'Green'],
	'm',
	$_[1].PadRight(10, ' '),
	[char]27,
	'[49m'
) | Write-Host -NoNewline
}

#$context = [System.Collections.Queue]::new()
$context = [PSCustomObject]@{
	Count = 0
	Index = 0
	Queue = @($NULL, $NULL, $NULL, $NULL, $NULL, $NULL)
} `
| Add-Member `
	-Name       Enqueue `
	-MemberType ScriptMethod `
	-Value      { Param($item)
		if ($this.Count -eq $this.Queue.Count) {
			throw $this.Count
		}
		$this.Queue[($this.Index + $this.Count) % $this.Queue.Count] = $item
		++$this.Count
	} `
	-PassThru `
| Add-Member `
	-Name       Dequeue `
	-MemberType ScriptMethod `
	-Value      { Param()
		if ($this.Count -eq 0) {
			throw $this.Count
		}
		$this.Queue[$this.Index++]
		$this.Index %= $this.Queue.Count
		--$this.Count
	} `
	-PassThru

$elipsed = @($False)
Function Context {
	for ($count = 0; $context.Count -and $count -lt 3; ++$count) {
		$line = $context.Dequeue()
		
		$line[0] | Output -colour Green
		'   ' | Write-Host -NoNewline
		
		$line[1] | Output -colour Green
		'' | Write-Host
	}
	if ($elipsed[0] = !!$context.Count) {
#		' ' * 61 + '...' | Write-Host -ForegroundColor Green
[char]27,'[32m',(' ' * 61),'...',[char]27,'[39m' -join ''
	}
}

'diff -y <(xxd "$1") <(xxd "$2")' `
| bash -s $args `
| %{
	$line = $_ -split '\t' -replace '(?<=  .{10}) \|',''

	if ($line[0] -eq $line[1]) {
		if ($context.Count -eq 6) {
			Context
		}
		$context.Enqueue($line)
		if ($elipsed[0]) {
			$context.Dequeue() | Out-Null
		}
	}
	else {
		Context
		
		$line[0] | Output -colour Red
		'   ' | Write-Host -NoNewline
		
		$line[1] | Output -colour Red
		'' | Write-Host
	}
}
Context

Once you have fixed your file, check what was missing:
vimdiff <(xxd FILE_rescued) <(xxd DIR/FILE)