disk utility – Secure erased drive – always one file can be found

I’ve been going through some old HD drives, secure erasing before sending to recycle. I periodically run Disk Drill over one of them, just to make sure I’m doing the job right.

No matter whether I do the ‘quick’ secure or the full-blown two day multiple run, Disk Drill always manages to find one plist fileā€¦ apparently the same file each time, or very similar. It appears to be some drive spec & prefs.

Could this be something to do with the EFI partition, generated as part of the new format, rather than anything left over from the old? I honestly can’t think of any reason it should always be able to find this & nothing else – oddly, even if the drive was previously NTFS. All the secure wipes are to GUID/HFS+, whatever they were formatted before. EFI is my only logical conclusion.
This is on Mojave, as can be seen from info in the plist file below.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Annotations</key>
    <dict>
        <key>Creation_Predicates</key>
        <dict>
            <key>false</key>
            <integer>0</integer>
            <key>fstype.hfs</key>
            <integer>1</integer>
            <key>has.uuid</key>
            <integer>1</integer>
            <key>interconnect.usb</key>
            <integer>1</integer>
            <key>is.alreadyindexed</key>
            <integer>0</integer>
            <key>is.apfssnapshot</key>
            <integer>0</integer>
            <key>is.automount</key>
            <integer>0</integer>
            <key>is.backupstore</key>
            <integer>0</integer>
            <key>is.backupvolume</key>
            <integer>0</integer>
            <key>is.bootablevolume</key>
            <integer>0</integer>
            <key>is.cameramedia</key>
            <integer>0</integer>
            <key>is.diskimage</key>
            <integer>0</integer>
            <key>is.dontbrowse</key>
            <integer>0</integer>
            <key>is.ejectable</key>
            <integer>0</integer>
            <key>is.external</key>
            <integer>1</integer>
            <key>is.externalvolumes.defaultoff</key>
            <integer>0</integer>
            <key>is.externalvolumes.ignore</key>
            <integer>0</integer>
            <key>is.filevault</key>
            <integer>0</integer>
            <key>is.forcedefaultindex</key>
            <integer>0</integer>
            <key>is.forcefsonly</key>
            <integer>0</integer>
            <key>is.home</key>
            <integer>0</integer>
            <key>is.internal</key>
            <integer>0</integer>
            <key>is.ipod</key>
            <integer>0</integer>
            <key>is.local</key>
            <integer>1</integer>
            <key>is.lowdiskspace</key>
            <integer>0</integer>
            <key>is.mobilebackups</key>
            <integer>0</integer>
            <key>is.network</key>
            <integer>0</integer>
            <key>is.nonSearchableRole</key>
            <integer>0</integer>
            <key>is.quarantined</key>
            <integer>0</integer>
            <key>is.readonly</key>
            <integer>0</integer>
            <key>is.removable</key>
            <integer>0</integer>
            <key>is.rootfs</key>
            <integer>0</integer>
            <key>is.safeboot</key>
            <integer>0</integer>
            <key>is.syntheticmount</key>
            <integer>0</integer>
            <key>is.tinyvolume</key>
            <integer>0</integer>
            <key>is.windowsbootablevolume</key>
            <integer>0</integer>
            <key>is.xsan</key>
            <integer>0</integer>
            <key>policy.location.volume</key>
            <integer>1</integer>
            <key>self.appleinternal</key>
            <integer>0</integer>
            <key>self.server</key>
            <integer>0</integer>
            <key>status.neverindex</key>
            <integer>0</integer>
            <key>supports.catsearch</key>
            <integer>1</integer>
            <key>supports.fileids</key>
            <integer>1</integer>
            <key>supports.volfs</key>
            <integer>1</integer>
            <key>true</key>
            <integer>1</integer>
            <key>uuid.b988bc99-b85b-332d-bd6e-6f7bac8cdd28</key>
            <integer>1</integer>
        </dict>
        <key>DebugKey1</key>
        <string>2021-07-17 3:41:10 pm +0000 3</string>
        <key>DefaultStore_EffectiveSearch</key>
        <integer>3</integer>
        <key>DefaultStore_RequestedSearch</key>
        <integer>3</integer>
    </dict>
    <key>ConfigurationCreationDate</key>
    <date>2021-07-17T15:41:10Z</date>
    <key>ConfigurationCreationVersion</key>
    <string>Version 10.14.6 (Build 18G9216)</string>
    <key>ConfigurationModificationDate</key>
    <date>2021-07-17T15:41:10Z</date>
    <key>ConfigurationModificationVersion</key>
    <string>Version 10.14.6 (Build 18G9216)</string>
    <key>ConfigurationVolumeUUID</key>
    <string>B988BC99-B85B-332D-BD6E-6F7BAC8CDD28</string>
    <key>ConfigurationWriteback</key>
    <false/>
    <key>Exclusions</key>
    <array/>
    <key>Options</key>
    <dict>
        <key>ConfigurationType</key>
        <string>Default</string>
    </dict>
    <key>Stores</key>
    <dict>
        <key>E0FD820A-A9A6-4118-A1E0-36DDC4458E36</key>
        <dict>
            <key>CreationDate</key>
            <date>2021-07-17T15:41:10Z</date>
            <key>CreationVersion</key>
            <string>Version 10.14.6 (Build 18G9216)</string>
            <key>IndexVersion</key>
            <integer>95</integer>
            <key>PartialPath</key>
            <string>/</string>
            <key>PolicyDate</key>
            <date>2021-07-17T15:41:10Z</date>
            <key>PolicyLevel</key>
            <string>kMDConfigSearchLevelReadWrite</string>
            <key>PolicyProcess</key>
            <string>STORE_ADD</string>
            <key>PolicyVersion</key>
            <string>Version 10.14.6 (Build 18G9216)</string>
        </dict>
    </dict>
</dict>
</plist>