It's not Power Pro's mistake. I have a reel spooler with a line counter and have spooled dozens of reels with dozens of line types and sizes. many reels - ABUs, many Shimanos, Diawas, Quantums and Floogers. Many lines-Trilene XL, Big Game, Super braid, Ande, Power Pro, Gorilla Braid, Vanish, P-line, Yo-Zuri and others. I have yet to see a reel hold as much line as it says it should and still cast properly. They all seem to exagerate line capacity. Maybe its marketing or maybe a bad conversion from metric units, but it seems to be consistent.
I would worry more with my typical casting distance and how the line fills my spool to the proper casting diameter of the reel spool. I hope this makes sense.
The good news is, as modern lines get better and more expensive, with a little quality backing you can get two spools out of one spool pacakge. JMHO
Ronnie