Mark, this is another case where Scripture is incomplete. It is a story told by eye witnesses decades after the fact. There are minor differences in detail, yet none can say that the differing accounts of Matthew, Mark, Luke and John perjured themselves or the Lord. John tells us that the message was placed there at the command of Pilate himself and was done over the objections of the Chief Priest. It tells us more of the mind of the Romans than the Holy Spirit. This sinner's conclusion is that this point is not important to the Gospel message.
Jesus' sacrifice was to gather and unite us. How sad that we use it to divide us.
And this sinner agrees with you. It is just so interesting to see that those who hang their hats on the peg of sola scriptura violate that principle with reckless abandon, while never admitting it.