For the date-time case that might be more specific, since we are only expecting these errors from iso8601, and any others that appear is probably due to our code and may deserve a 500.  :)  It's up to you though.  None of this is particularly ideal, but perhaps when we have some time we can come back to this.

Would you mind terribly also filing a low priority task to check on the progress of these issues, so we don't forget it?  This otherwise LGTM