So I was trying to track down any scientific studies I could find on the A. Crassipinnis. Most any study I could find mentioning this oscar type cite Sven O Kullander's 1986 study:
Cichlid fishes of the Amazon River drainage of Peru. This includes studies I could find published up until 2013 (from the database I have access too). It is in this study where you find the measurement of "240 mm" (p,. 71) which is where all the popular sites (like Wikipedia) repeat ad infinitum as 24 cm or a little less than 10". So yes, as Kevin mentioned, we shouldn't always trust Wikipedia, but in fact, this measurement comes from this published, peer reviewed studied. However, Kullander calls these measurements "provisional" and says that more data is needed (which as far as I can tell no one has actually published). Given Kevin's experience collecting and handling these fish (in the hundreds) it is certainly seems that this study (35 years old) is in need of an update. I'd be happy to know if anything has been published.
Both Daivd's and my Oscars, if they are to be classified as A. Crassipinnis, far exceeded this established "maximum" size. Darth grew to 13" and I think Chunk grew to a similar size. We were told they were "A. Orbicularis" at the time we received ours (around 2014) which I have never found a study on so was never really more than a selling point it seems. In any case Kevin has reasonably conflated and corrected this misnomer to A. Crassipinnis.
Anyway, here is a PDF link to Kullander's seminal if somewhat outdated study from 1986. Would be happy if anyone had more sources to link us all too.