The 1914 was not in fact worked out by Russell but by Barbour who was his teacher also the invisible return pretext was formulated by a second adventist follower of Barbour and then taken over by the dubs to this day.
It was a cunning way to cover up their repeated and embarassing prophetic failures which the JWs were to perpetuate to this day: "it happened but we couldn't see it because it was invisible.", it's an easy way to deceive those who can't check out what's going in the invisible realm. Plus the idea is unbiblical nowhere do we find an invisible return to be later followed by a visible one. There is going to be one very visible return with the sign of man in heaven for all to see. The Christ has always been invisibly present.