I was hoping someone could help explain (a little more) the differences between these two types of circumstancing found in the SAE course:
(from Student Guide)

Date property — the rule variant is effective whenever the value of a date property satisfies the
circumstancing condition. This condition can be either a single date or a range of dates. If the value
of the property is later than the specifies date or falls within the range of dates, the application uses
the circumstanced variant of the rule, rather than the base rule.
As-of date — the rule variant is effective after a certain date, or during a range of dates. After the
specified date or during the specified range, the application applies the circumstanced variant of
the rule, rather than the base rule.