My website is implemented through Hugo, with content sources in Markdown. Metadata is added through a so-called "front matter" header within Markdown files. I noticed date metadata (front matter) was missing on content pages and consequently had 2001 on RSS feeds.

I used Nushell to en-mass add page dates after-the-fact, with date values determined through Git.

# Determine pages with missing date front matter (may be missing pages that have `date = ` as content)
glob **/*.md | where {|x| $x | open | not ($in | str contains 'date = ') } | save missing.json

# Determine content creation dates through Git add authoring date
open missing.json | wrap path | upsert date {|x| git log '--follow' '--diff-filter=A' '--format=%ad' '--date=iso' '--' $x.path | into datetime } | save dates.json

# Prepend date TOML front matter to closing fence
open dates.json | each {|x| $x.path | open --raw | str replace "\r\n+++\r\n" $"\r\ndate = \"($x.date | format date '%Y-%m-%d %H:%M:%S')\"\r\n+++\r\n" | collect | save -f $x.path }

Example [inline] result/fixup:

date = "2022-08-07 18:31:18"
+++

Some work details and manual cleanup (e.g. pages with resource front matter where the date declaration must be placed before them) omitted.