Events Invitation and Registration Dates are currently not available in default sets. This is inconsistent with other available fields, and would be useful to have.
Response Date is available on the default set, as is Invitation or Registration status (Do Not Invite, Not Invited, Invited or Do Not Register, Not Registered, Restered).
It would seem logical, if we're able to define a default Registration or Invitation status, we should be able to include their associated dates.
And for that matter, make registration units a default option as well!