This is something no one else has ever done right and many people use b2evolution just for this single feature alone:

b2evolution remembers ALL the slugs, past and present, of ALL your posts/pages/articles.

And, then no matter which URL scheme you use in the future, b2evolution will automatically redirect all your old URLs to the current canonical URL of each post/page/article.

For example, you could have a post that currently resides under https://www.mysite.com/xyz/current-slug-of-article

But in the past that article has used the slug old-slug-of-article as well as old_article_slug. It may even have has a short slug like short-slug.

b2evolution has the memory of all old slugs (which can also be imported from WordPress or Markdown). This allows b2evolution to automatically catch any old URL such as:

• https://www.mysite.com/xyz/old-slug-of-article
• https://www.mysite.com/xyz/old_article_slug
• https://www.mysite.com/xyz/short-slug

or even:

• https://www.mysite.com/old-slug-of-article
• https://www.mysite.com/old-article-slug
• https://www.mysite.com/short-slug

or even:

• http://mysite.com/old-slug-of-article
• http://mysite.com/old_article_slug
• http://mysite.com/short-slug

or even:

• http://any.sub.domain.mysite.com/any/structure/you/like/old-slug-of-article
• http://any.sub.domain.mysite.com/any/structure/you/like/old_article_slug
• http://any.sub.domain.mysite.com/1984/short-slug

And ALL of these will be redirected to the current URL of your post, in this case https://www.mysite.com/xyz/current-slug-of-article.

This is because b2evolution uses unique slugs per post/page/article and by default remembers all changes.

More info: Managing Item Slugs