You did have 100% coverage back then, but not high quality all of the time. In some rare cases only a single satellite pseudofix would have been available. That

You did have 100% coverage back then, but not high quality all of the time. In some rare cases only a single satellite pseudofix would have been available. That can still be accurate if the location device carries a decent synchronized clock. IOC was defined as always being in sight of 3 or more satellites, plus maintenance capability. That was achieved in 1993.