Culture Nine

Why are September, October, November and December considered the 9th, 10th, 11th and 12th months?

From the Latin cardinal prefixes:

Septi- = seven

Octo- = eight

Novem- = nine

Dec- = ten

Thus linguistically, September should be the 7th month, October the 8th month, November the 9th month, and December the 10th month.

The Rule of Five is as followed:

In all Shakespearean Tragedies there are exactly five on stage deaths (no more, no less) provided that:

1. The character(s) must be alive at the beginning of the play.

(i.e. not Hamlet's father in Hamlet)

2. The character(s) must have at least one speaking part in the play.

(i.e. not the framed "murderers" in Macbeth and the non-speaking conspirators in Julius Caesar)

3. The character(s) must be killed on stage or be killed offstage within one scene (i.e. Duncan's murder).

(i.e. not Cicero or Portia in Julius Caesar)

Following these constraints, do all Shakespearean Tragedies follow the Rule of Five?

Examples:

Julius Caesar: Caesar, Cinna the Poet, Cassius, Titinius, Brutus

Macbeth: Duncan, Banquo, Lady Macbeth, Young Siward, Macbeth

Romeo & Juliet: Mercutio, Tybalt, Paris, Romeo, Juliet

If the Rule of Five is TRUE, please provide a possible explanation for this format.

If the Rule of Five is UNTRUE, please provide a counterexample.