The unchanging part of the teaching is the existence of purgatory, not in the inference as to its nature or essence. Too many people compare minutia for existence of contradiction in different teachings to either pit one pope against another or to invalidate this or that council.
The pamphlet is an example of the legalism and mostly “negative”, as in lacking positive attributes and focusing on the prohibitions, which were part of the mindset of the day. Vat II made this legalism a major point in reforming the Church, and as the Bible shows, Jesus’ teaching is more positive as in gaining heaven and virtue rather than avoiding sinners, following the legalism of the Pharisees, or seeing sin in those physically afflicted. This is the major teaching of the wisdom and priestly sections of the Old Testament, Psalms, Proverbs, Wisdom, etc.
Jesus just didn’t make stuff up or present teachings that were innovative or that the Pharisees couldn’t have known by desiring to do God’s Will. His teaching seen in the New Testament is the fulfillment of Old Testament teaching, and it was the human nature of the Pharisees that erred, in the same way the Church had to be reformed of this at Vat II. Union with God is more about what you should do than about what you shouldn’t, but the negative attributes should not be abrogated as some, in overreaction to accentuating the positive, have done.
Those who say the ejaculations[prayers] 1,000 times a day gain 300,000 days Indulgence! What a multitude of souls they can thus relieve! What will it not be at the end of a month, a year, 50 years? And if they do not say the ejaculations, what an immense number of graces and favors they shall have lost! It is quite possible – and even easy – to say these ejaculations 1,000 times a day. But if one does not say them 1,000 times, let him say them 500 or 200 times.
An example of negation and legalism. Why not 24/7 of purgatory prayer? Because union with God through the Holy Spirit in your soul is most important to sanctification. Miss out on this and you will be lucky to get to use your indulgence to get out of purgatory as you will have no divine life in your soul to even make “final cleansing” necessary. In contrast to the errors of those who don’t follow the Magisterial teaching of the Church, is the myriad of theological brilliance in the likes of “Theology of the Body”, Veritatis Splendor, Fides et Ratio, Spe Salvi and Deus Caritas Est.
The Divine Mercy diary of St. Faustina no. 741 describes the reality of hell but the words of Jesus are far from negative and focus on the positive Love of God, trust, and hope. There is not much hope in prohibitions, but plenty of fear. You can lose the fear of God in His infinite Divine Mercy.