Post Publish Date Different than Sitemap Publish Date

Hello,

We’re noticing that several of the post publish dates are different than what shows up on the sitemap. We have revisions turned off, so I am not sure if this has to do with edits, though I thought that that date wouldn’t change:

• https://www.shipworks.com/blog/shipworks-2017-trade-show-schedule/
  Xml sitemap date: 4/3/2017
  Published on: 2/23/17
• https://www.shipworks.com/blog/best-rate-easily-compare-shipping-carrier-rates/
  Xml sitemap date: 4/3/2017
  Published on: 3/17/17
• https://www.shipworks.com/blog/free-webinar-solving-the-top-5-challenges-facing-warehouse-managers-in-2017/
  Xml sitemap date: 1/26/2017
  Published on: 1/17/17
• https://www.shipworks.com/blog/shipworks-to-support-usps-automated-package-verification/
  Xml sitemap date: 2/6/2018
  Published on: 7/25/2017

The page I need help with: [log in to see the link]