Infallibility?! On what grounds?!

I once understood that a Pope speaks infallibly only ex cathedra, when making a formal statement of doctrine with the utmost solemnity, from the chair of Peter. I understood Pius XII's proclamation of the Assumption to be the last occasion on which this happened.

When, in 2012, is infallible infallible?

In his comment to Cardinal Re regarding the ordination of women, Pope Benedict writes "... the Holy Father John Paul II decided in an infallible and irrevocable way that the Church does not have the right to ordain women to the priesthood."

Infallible and irrevocable?

Can infallible be revoked, then? Pope Benedict seems to refer to John Paul II's Apostolic Letter of 22 May 1994,Ordinatio Sacerdotalis: "Wherefore... I declare that the Church has no authority whatsoever to confer priestly ordination on women and (that) this judgement is to be definitively held by all the Church's faithful."

• If this is an infallible statement, may I respectfully ask how?
• Can a Pope declare his own statements to be infallible?
• Can a Pope retrospectively declare a predecessor's statements to be infallible?
• Are papal statements in an apostolic letter infallible, as above?
• What about papal statements in an encyclical letter? All of them? Or only some?
• Can the Curia (the Magisterium?) declare a statement infallible?
• What about an Ecumenical Council of the Church?
• What about the People of the Church, perhaps by acclaim?

I wonder whether such confusion is generated at the centre in the interests of control.

John Merrigan, East Molesey, Surrey