Every delivery leaves the plant with a test certificate, and most of them are filed without being read. Three numbers on it decide whether the units are right for the wall they are going into.
Compressive strength is reported as an average of the units tested, with the individual minimum alongside it. The average is what the specification quotes; the individual minimum is what tells you how consistent the batch was. A high average hiding a low individual result is a batch with a mixing problem, not a batch that passed.
Water absorption, given as a percentage by mass, predicts how the wall will behave rather than how it will stand. Below about 6% the unit resists driving rain and carries plaster without drinking the mix dry. Above 10% expect efflorescence and a plasterer asking for more water.
Density ties the other two together. It is the number that explains an anomaly: a unit that is strong but absorbent was probably compacted well and cured short. Read all three, and read them against the batch date on the top line.