Should I submit a sitemap with only new links added?

The Google documentation says there's a limit of 50k URLs in sitemaps you send to them, and I want my sitemap to be submitted by an automated job periodically. Therefore, shouldn't I just have 开发者_C百科the sitemap contain only the N most recent URLs added to my site? Yes, I know you can have multiple sitemaps, and I do have a separate one for the static HTML pages in the site. But I also need one for the database content that may not be reachable in one hop from the main pages, and I don't like the idea of a growing list of sitemaps(It may sound like 50k is more than enough, but I don't want to code with that assumption).

Sure - if you know your previous pages (from an older sitemap.xml or simply crawled) are indexed, you should be fine by including only new links.