  The microlensing surveys MACHO, EROS, MOA and OGLE (hereafter called MEMO)
have searched for microlensing toward the Large Magellanic Cloud for a
cumulated duration of 27 years. We study the potential of joining these
databases to search for very massive objects, that produce microlensing events
with a duration of several years. We identified the overlaps between the
different catalogs and compiled their time coverage to identify common regions
where a joint microlensing detection algorithm can operate. We extrapolated a
conservative global microlensing detection efficiency based on simple
hypotheses, and estimated detection rates for multi-year duration events.
Compared with the individual survey searches, we show that a combined search
for long timescale microlensing should detect about ten more events caused by
$100.M_{\odot}$ black holes if these objects have a major contribution to the
Milky Way halo. Assuming that a common analysis is feasible, meaning that the
difficulties that arise from using different passbands can be overcome, we show
that the sensitivity of such an analysis might enable us to quantify the
Galactic black hole component.
