The IAU Minor Planet Center lists $(486958)\space 2014 \space MU_{69}$ "Ultima Thule" as having an uncertainty parameter of 2, based on the observation arc of 851 days, from its discovery in 2014, to the last observation submitted from Hubble in 2016.

Other sources indicate that there have been a number of ground-based observations of Ultima Thule occulting various background stars. Are these "observations" purposely not included/submitted as further sightings to increase the observation arc?

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    $\begingroup$ Have a look at this answer to Does JPL's Horizons have better MU69 state vectors for the New Horizons flyby somewhere? $\endgroup$
    – uhoh
    Commented Jun 7, 2019 at 21:56
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    $\begingroup$ This doesn't directly answer the question, but Porter et al. 2018 tell how they determined 2014 MU69's orbit well enough to predict occultations. $\endgroup$
    – Mike G
    Commented Jun 13, 2019 at 4:07


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