Old Light, New Light
It would seem as we look back at Watchtower beliefs, particularly since they took the name: Jehovah's Witnesses, that they are guilty of flip-flopping and using Proverbs 4:18 as their reason for doing so. When we look at the following quote, it would seem that the Society's leadership would light a gas jet to see a few feet in front of them, as they light the next one they turn off the previous ones, so that at any given time they only have enough light to see a few feet. Had they heeded the counsel of Pastor Russell they would see that instead of "substituting" they see "the true increase is by adding to, not by substituting one for another"
"If we were following a man undoubtedly it would be different with us; undoubtedly one human idea would contradict another and that which was light one or two or six years ago would be regarded as darkness now: But with God there is no variableness, neither shadow of turning., and so it is with truth; any knowledge or light coming from God must be like its author. A new view of truth never can contradict a former truth. "New Light" never extinguishes older "Light," but adds to it. If you were lighting up a building containing seven gas jets you would not extinguish one every time you lighted another, but would add one light to another and they would be in harmony and thus give increase of light; So is it with the light of truth; the true increase is by adding to, not by substituting one for another" [ZWT, 02/1881, pg. 188]