[std] might and could: re-review for complicated cases

[meta.rqmts] p5

that instantiation would yield a different result if performed in a context where T were a complete type

"yield a different result" -> "the validity or meaning of the instantiation depends on the completeness of T"; run by CWG / LWG.

[time.zone.info.sys]

A correct offset for the \tcode{time_zone} off daylight saving time
can be obtained by querying the \tcode{time_zone} with a \tcode{time_point}
that returns a \tcode{sys_info} where \tcode{save == 0min}.
There is no guarantee
what \tcode{time_point} (if any) returns such a \tcode{sys_info}
except that it is guaranteed not to be in the range \range{begin}{end}
(if \tcode{save != 0min} for this \tcode{sys_info}).

Review the quoted [meta.rqmts] p5 and [time.zone.info.sys] wording in the C++ draft. Start with the surrounding standard text and the CWG/LWG context mentioned for the first change, then examine the time-zone guarantee in [time.zone.info.sys]. Done means the complicated cases are resolved and the resulting wording is reflected in the draft.