The paper considers global tendencies of the GNSS high-accuracy service evolution. Key performance characteristics defined and the method of their estimation is proposed based on orbit and clock data only. The description of the pseudo-range and pseudo-phase measurement model used in the formation of the reference ephemeris-time information on the global network of stations is presented. The results of the high-accuracy a posteriori orbit and clock data comparison are presented for several analysis centers. In addition, the results of the real-time performance assessment based on the proposed method are also presented. Comparison with the consumer level processing data from the global stations network shows that all the estimates obtained through the proposed methodology are apparently positive. Despite this, the proposed technique can be used to determine the signal-in-space ranging error for one or several GNSS without real user measurements.