TeraByte Unlimited

The preface:

I'm running IFW 3.38. I created a full backup yesterday, using the command line options:

/wait /b /d:w0 /f:D:\TeraByte_TBI_Backups\Drive=$~DN$-Date=$~YYYY$-$~MM$-$~DD$@$~HHMM$--------Full /savename:lastfullbackup /v /vb /comp:10 /hash

The backup file was named:

Drive=0-Date=2020-04-28@1807-----Full.TBI

The "lastfullbackup" registry value was created, with its data set to:

D:\TeraByte_TBI_Backups\Drive=0-Date=2020-04-28@1807-----Full

The issue:

I just ran a backup, using the command line options:

/wait /b /base:$~lastfullbackup$ /f:"D:\TeraByte_TBI_Backups\Drive=$~DN$-Date=$~YYYY$-$~MM$-$~DD$@$~HHMM$" /v /vb /comp:10 /hash /filetpl:"Drive=$~DN$-Date=$~YYYY$-$~MM$-$~DD$@$~HHMM$"

The backup file was named:

Drive=-Date=2020-04-29@1842.TBI

Please advise on why the drive number would be missing in the differential backup file name.

Updating IFW is an inconvenience and a risk, and I don't like to do it without a good reason. Has this issue been addressed since IFW 3.38?

Release notes say:
NOTE: If using incrementals/differentals for GPT drives with a Windows RE or Intel RST partition then you will need to create a new full.

I don't see how that pertains to my issue. In any case, I've simply stopped using $~DN$.