I’ve never heard any believer refer to a second book of the Bible as “two”.
*******************************************************
Really? I hear it at Sunday School, church and prayer meetings on Wednesday, every week.
If someone says “Corinthians”, how would you know which book they were referring to? 1 John, 2 John, 3 John.
I have often used One Corinthians or Two Corinthians with the hand signal indicating 1 or 2 when teaching Sunday School which I did for many years.