The first two words of 5:20, the third-person imperative and the demonstrative pronoun (γινωσκέτω ὅτι ginōsketō hoti) would seem to be the original reading and were altered to the second-person plural imperative (γινώσκετε ginōskete).
"Copyists were perplexed, not knowing whether ψυχὴν αὐτοῦ (his soul) referred to the soul of the person converted or to the soul of the person who converted someone else."
This textual variant would be listed as a significant one. Textual scholar Daniel Wallace writes, “A textual variant is simply any difference from a standard text (e.g., a printed text, a particular manuscript, etc.) that involves spelling, word order, omission, addition, substitution, or a total rewrite of the text.”
In the New Testament, we have numerous instances where the missing verse(s) evidently have come from other NT books or other parts of the same book itself.
Whose fault is it that the churchgoer for decades has been less informed about the Bible that they carry than the atheists, Muslims, Mormons, Jehovah's Witnesses, and the Skeptics?
Textual variants in the New Testament are the subject of the study called textual criticism of the New Testament. Textual variants in manuscripts arise when a copyist makes deliberate or inadvertent alterations to a text that is being reproduced.
Wettstein rendered service to textual criticism by his collection of various readings and his methodical account of the manuscripts and other sources.
The sad state of affairs is that textual scholarship as a whole is unwittingly or knowingly moving the goalposts for some unknown reason. In textual criticism, it is now the earliest knowable text, the sociohistorical approach to New Testament Textual Studies, and, the newest trend of trying to redate our earliest NT papyri.