I agree with this, and especially if your tap water parameters are hard, and mineral rich.
It is very difficult to judge size by various aquarists viewpoints.
One aquarist might do only a once per week 50% water change, and thus have a smaller, slower growing specimen, than an aquarist that does 3 or 4, 40% water changes per week.
And although smaller, the aquarist that does only 1 water change per week might end up with a HITH chronically scarred individual as maturity sets in, as opposed to the 3 per week water change providing a totally healthy P-Bass.
One aquarist may provide perfect water parameters as far as mineral content, someone in another city, may not.
You may also consider that some literature may use "standard length" when quoting a size (not including the tail in the measurement), as opposed to "total length" which includes the tail, often an extra 6". And when providing for an aquarium specimen "Total Length" should be the criteria, not simple standard length.
One other thing to consider about water parameters.
P-bass have introduced to the hard waters of Lake Gatun in Panama and get about 1/3 smaller than the soft water Amazonian species.
But they were introduced around 1960 so have had 60+ years, and many generations to adapt to those foreign water parameters.
Consider how many died evolving to that adaptation.
