Age range of radiocarbon dating
The very specific band of /- margins of error mentioned, all between 47 and 58 years on each side, correspond result of a C-14 test and, specifically, to the 1-sigma confidence level that is used to express radiocarbon age results. Jull, “Accelerator radiocarbon dating of art, textiles, and artifacts,” in Nuclear News (June 1998).For such figures, we should expect a figure between 40 and 60 years on each side, as Jull’s own publication record bears out: “The AMS method has generally improved since its inception, so that external precision of about ±0.5 percent in 14C content, or ±40 years in uncalibrated radiocarbon age are possible on 1-mg-sized samples.” “For radiocarbon ages, errors of about ±50 years on recent material are typical for accelerator measurements.” – A. The use of /- expressions (“plus or minus”) is also consistent with the idea that we are seeing (uncalibrated) “radiocarbon years” here.
The Wikipedia page on Radiocarbon dating actually seems to be fairly good and goes over some of the potential pitfalls involved in radiocarbon dating.
The most detailed account of the C-14 carbon dating results for the Gospel of Judas manuscript in Codex Tchacos, of which I am aware, is found in the book by journalist Herbert Krosney, The Lost Gospel: The Quest for the Gospel of Judas Iscariot, published by National Geographic (April 6, 2006).