Every few years, NGS reprocesses all CORS data collected since 1994 to compute provisional positions and velocities
for all CORS relative to the current ITRF realization: call it ITRFxx. If,
for any station, these provisional ITRFxx positional coordinates differ
from the currently adopted ITRFxx positional coordinates by more than 1 cm in the north-south or east-west component
or by more than 2 cm in the vertical component, then NGS adopts the provisional position and velocity to supersede
the previously adopted ITRFxx position and velocity.