Specifically without the last modified timestamp we violate this aspect of the license:
"Attribution—You must attribute the work in the manner specified by the author or licensor (but not in any way that suggests that they endorse you or your use of the work.)"

I'm not sure why the last modified timestamp is not changing. This may be related to the templates used but not the page or some kind of bug.

Also see:
https://en.wikipedia.org/wiki/Wikipedia:Village_pump_(technical)#Offputting_message

The tiemstamp shown is one of the last revision on the page. When templates are changed, this timestamp is not updated. I recommend just changing the date to "history" on main page.

That sounds like a good idea. I would suggest Page History or Article History or Revision History so the context is clear.

Change 79276 had a related patch set uploaded by Jdlrobson:
Bug 51924: Special case main page history link

https://gerrit.wikimedia.org/r/79276

Change 79276 merged by jenkins-bot:
Bug 51924: Special case main page history link

https://gerrit.wikimedia.org/r/79276