Q: How do I actually build a redirect map without missing pages?

Q: How do I actually build a redirect map without missing pages?

Good question — guessing here is what tanks traffic. Here's a repeatable process.

Short answer: don't redirect from your sitemap, redirect from reality.

Long answer, in order:
— Pull old URLs from three sources, not one: your XML sitemap, a full Screaming Frog crawl, and your server access logs (last 90 days). Logs catch URLs nothing links to anymore but Google still hits.
— Add GSC's 'Pages' export and your top 500 by backlinks (from any link tool).
— Dedupe into one spreadsheet. Column A = old URL, column B = best new URL, column C = match confidence.
— Map one-to-one by content, never default everything to the homepage.
— Flag anything low-confidence for manual review.

Next step: get that combined list to ~95% coverage before you write a single redirect rule.