Editorial: Clarify invariant that ISO Date Records are always valid

And fix typo

Author: aria-eide

spec/plaindate.html

@@ -571,6 +571,7 @@ <h1>ISO Date Records</h1>
       <p>
         An <dfn variants="ISO Date Records">ISO Date Record</dfn> is a Record value used to represent a valid calendar date in the ISO 8601 calendar, although the year may be outside of the allowed range for Temporal.
         ISO Date Records are produced by the abstract operation CreateISODateRecord.
+        For any ISO Date Record _d_, IsValidISODate(_d_.[[Year]], _d_.[[Month]], _d_.[[Day]]) must return *true*.
       </p>
       <p>ISO Date Records have the fields listed in <emu-xref href="#table-temporal-iso-date-record-fields"></emu-xref>.</p>
       <emu-table id="table-temporal-iso-date-record-fields" caption="ISO Date Record Fields">

spec/plaindatetime.html

@@ -678,7 +678,7 @@ <h1>Abstract Operations</h1>
       <h1>ISO Date-Time Records</h1>
       <p>
         An <dfn variants="ISO Date-Time Records">ISO Date-Time Record</dfn> is a Record value used to represent a valid calendar date in the ISO 8601 calendar together with a clock time.
-        For any ISO Date-Time Record _r_, IsValidISODate(_r_.[[ISODate]].[[Year]], _r_.[[ISODate]][[Month]], _r_.[[ISODate]].[[Day]]) must return *true*, and IsValidTime(_r_.[[Time]].[[Hour]], _r_.[[Time]].[[Minute]], _r_.[[Time]].[[Second]], _r_.[[Time]].[[Millisecond]], _r_.[[Time]].[[Microsecond]], _r_.[[Time]].[[Nanosecond]]) must return *true*.
+        For any ISO Date-Time Record _r_, IsValidISODate(_r_.[[ISODate]].[[Year]], _r_.[[ISODate]].[[Month]], _r_.[[ISODate]].[[Day]]) must return *true*, and IsValidTime(_r_.[[Time]].[[Hour]], _r_.[[Time]].[[Minute]], _r_.[[Time]].[[Second]], _r_.[[Time]].[[Millisecond]], _r_.[[Time]].[[Microsecond]], _r_.[[Time]].[[Nanosecond]]) must return *true*.
         It is not necessary for ISODateTimeWithinLimits(_r_) to return *true*.
       </p>
       <p>ISO Date-Time Records have the fields listed in <emu-xref href="#table-temporal-iso-date-time-record-fields"></emu-xref>.</p>