[Spice_discussion] how are the long-term predicts made for ITRF93?

[Goodson, Troy D (US 392C)]

The tutorial https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/Tutorials/pdf/individual_docs/23_lunar-earth_pck-fk.pdf
as well as https://naif.jpl.nasa.gov/pub/naif/generic_kernels/pck/aareadme.txt
describe long-term predicts for ITRF93:

   Low accuracy, long term predict kernel. The extended predict region of this
   kernel---the time interval following the end of the predict region of the
   input EOP file---does not estimate changes in UT1-TAI. The dates in the
   file name are the file's coverage start and stop times:

      earth_200101_990628_predict.bpc


But, I believe IERS only provides predicts for 1 year. See https://www.iers.org/IERS/EN/DataProducts/EarthOrientationData/eop.html
and EOP2 files from https://eop2-external.jpl.nasa.gov are only predicted for about 78 days.

What is the source for the long-term prediction in a BPC kernel like earth_200101_990628_predict.bpc?

Thanks,

Troy.
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