  In this work, we update and develop algorithms for KMTNet tender-love care
(TLC) photometry in order to create an new, mostly automated, TLC pipeline. We
then start a project to systematically apply the new TLC pipeline to the
historic KMTNet microlensing events, and search for buried planetary signals.
We report the discovery of such a planet candidate in the microlensing event
MOA-2019-BLG-421/KMT-2019-BLG-2991. The anomalous signal can be explained by
either a planet around the lens star or the orbital motion of the source star.
For the planetary interpretation, despite many degenerate solutions, the planet
is most likely to be a Jovian planet orbiting an M or K dwarf, which is a
typical microlensing planet. The discovery proves that the project can indeed
increase the sensitivity of historic events and find previously undiscovered
signals.
