Preserving exact date in YAML headers (including time), and adding "canonical" HREF pointer for SEO in generated Tumblr pointer files. Also added "noindex,follow" tag for robots.
Preserving original Tumblr URL in YAML header. Could be made into an option, but doesn't hurt and good for future redirect efforts.
Fixing HTML quotes in redirect <meta> tag.
Adding optional "index.html" file in /post/ID/ folder, for better SEO.

Tumblr doesn't discriminate by "slug" text. While it's not possible at the current time to do rule-based redirects on some hosts (such as GitHub Pages) ... this will at least prevent search-engines from stacking up a bunch of 404's checking that directory.

Unfortunately, there is still no way for hosts like GitHub Pages to do "catch-all" slug text, unlike Tumblr. So, people with messed up links to your blog that used to work will still return 404 unless they've simply left off the slug text.
Removing overkill <meta> tag. May hide pages temporarily from Google Search.

https://productforums.google.com/d/msg/webmasters/0sqRrolO_Ss/igOdQIjwKdEJ

"One reason for this is that we sometimes find a non-canonical URL first. If this URL has a noindex robots meta tag, we might decide not to index anything until we crawl and index the canonical URL. Without the noindex robots meta tag (with the rel=canonical link element) we can start by indexing that URL and show it to users in search results. As soon as we crawl the canonical URL, we can change to the canonical URL instead. It's also much safer because you don't have to worry about serving different versions of the content depending on the exact URL :-)."
Parse and output Tumblr dates with offset properly.

Ref. #54.