The positions and velocities of GNSS stations are occasionally affected by discontinuities. To account for these jumps, a piecewise linear model is used to describe station motions in the cumulative solution: one position+velocity set is estimated for each time period between two discontinuities. Note that successive velocities are usually constrained to be equal except when this would be unreasonable (such as following earthquakes).
The cumulative solution can thus contain several position+velocity sets per station. Each set is valid over a specific time period given in soln.snx. This file is updated when new discontinuities are detected during the weekly updates of the cumulative solution.
The residuals of the stacking are of particular interest since they depict station non-linear motions. Residual time series can be visualized and retrieved from the station pages of this website.