Keeping date of original recording in converted video file

Summary of workaround that seems to have worked:

• convert all files from .dv to .m4v using Handbrake and put the converted files in same directory as the original .dv files.
• use the command exiftool -DateTimeOriginal *.dv > filename.txt to extract the desired date information from the dv files and write it to an ascii file called filename.txt
• the output file (filename.txt) includes two lines per video file. The first line is the path to each file; the second line contains the relevant date&time metadata.
• open the filename.txt in a text/word editor and replace carriage returns between 1st and 2nd lines with a tab, so that each record is on a single line.
• open revised file in a spreadsheet; parse the data (text to columns); remove unwanted content so that the full filepath is in one column (e.g.file1.dv) and required date&time is in another column (e.g. yyyy:mm:dd hh:mm:ss),
• use concatenate command in a 3rd column to create a command of the form: exiftool -DateTimeOriginal="yyyy:mm:dd hh:mm:ss" "file1.dv". There will be one row for each file. Double quotes around file name can be omitted if there are no spaces in the path. then change all occurrences of .dv extensions within this file so that commands now read: exiftool -DateTimeOriginal="yyyy:mm:dd hh:mm:ss" "./directory1/file1.m4v"
• copy the contents of the 3rd column into terminal to put the required metadata into the m4v file.

Note:

1. the metadata tag DateTimeOriginal can be copied into a .mp4 file, but the tag is ignored when loading an mp4 file into FinalCutPro and FCP puts the file into an event based on the date the file was modified (typically the date of conversion to mp4).
2. in some .dv files, the DateTimeOriginal tag was not present, but FCP was apparently using the tag FileModifyDate if the tag DateTimeOriginal was missing. It seems I was fortunate in that the contents of FileModifyDate seemed to be the date the video was shot for almost all the files where the DateTimeOriginal tag was missing.
3. Be aware that adding when Exiftool adds an extra metadata tag, it creates a complete new copy of the file - even if disc is APFS - and therefore, at least temporarily, free space on the disc might be an issue.