Post Migration Errors - public action methods and controllers not found

Hi
Deployed a Nop customization a couple of days ago and getting tons of errors from Search Engines looking for pages that no longer exist:

A public action method 'xxx' was not found on controller ''Nop.Web.Controllers.xxx'.
The controller for path '/xxx/' was not found or does not implement IController.

Any suggestions for strategy for dealing with these more elegantly?

Will deal with asking search engines to reindex - not asking about that aspect.

Thanks!