Test cases for reduction generated using JPL Horizons.
The largest source of error will be DeltaT in the distant past. This mostly doesn't affect RA/Dec coordinates, but has an effect of many arcseconds on alt/az coordinates. This should still be acceptable for most applications for amateurs. The Moon also has a topocentric error of a few arcseconds even for modern dates, this is largely due to parallax effects since this does not implement sub-second corrections for UTC-UT1. Such corrections need daily updates from the IERS, and are not included here due to the constant updates required. Modern calculations for all planets and the Sun should be have sub-arcsecond accuracy, which approaches the limits of VSOP87's accuracy.