  Quantifying the captures of a URI over time is useful for researchers to
identify the extent to which a Web page has been archived. Memento TimeMaps
provide a format to list mementos (URI-Ms) for captures along with brief
metadata, like Memento-Datetime, for each URI-M. However, when some URI-Ms are
dereferenced, they simply provide a redirect to a different URI-M (instead of a
unique representation at the datetime), often also present in the TimeMap. This
infers that confidently obtaining an accurate count quantifying the number of
non-forwarding captures for a URI-R is not possible using a TimeMap alone and
that the magnitude of a TimeMap is not equivalent to the number of
representations it identifies. In this work we discuss this particular
phenomena in depth. We also perform a breakdown of the dynamics of counting
mementos for a particular URI-R (google.com) and quantify the prevalence of the
various canonicalization patterns that exacerbate attempts at counting using
only a TimeMap. For google.com we found that 84.9% of the URI-Ms result in an
HTTP redirect when dereferenced. We expand on and apply this metric to TimeMaps
for seven other URI-Rs of large Web sites and thirteen academic institutions.
Using a ratio metric DI for the number of URI-Ms without redirects to those
requiring a redirect when dereferenced, five of the eight large web sites' and
two of the thirteen academic institutions' TimeMaps had a ratio of ratio less
than one, indicating that more than half of the URI-Ms in these TimeMaps result
in redirects when dereferenced.
