Pope Benedict XV may not have denied that the Earth is geocentric, but that doesn't mean the 1616 decree was infallible. If it were, His Holiness or any of the other popes between 1757 and today would have noted as much.
No pope ever denied the infallibility of the definition and declaration of the anti-Biblical heresy of a fixed sun in 1616 by Pope Paul V and confirmed in 1633 by a second pope. All any pope did was to take heliocentric books off the Index. Pope Paul VI took all books off the Index but all the heresies in them remained heresies.
Very few know the details of the U-turn of 1820. Fr Olivieri, head of the Holy Office in 1820 admitted the 1616 decree was infallible. He knew this. So how then did Catholic churchmen have their infallible cake and eat it? He actually told his pope that the infallible decree of 1616 was a condemnation of a violent heliocentrism but that modern astronomers had confirmed heliocentrism of 1820 was a non-violent one. Obviously Olivieri had not read Copernicus's or Galileo's book in which both dismiss the old idea that if the Earth orbited all would be disturbed on its surface. This proves that Olivieri made up the lie about the infallible 1616 decree to leave it untouched.
And that is why the 1820 decrees allowing books to be read always made this clear:
1820 Decree states: ‘The Assessor of the Holy Office has referred the request of Giuseppe Settele, Professor of Astronomy at La Sapienza University, regarding permission to publish his work Elements of Astronomy
in which he espouses the common opinion of the astronomers of our time regarding the Earth’s daily and yearly motions, to His Holiness through Divine Providence, Pope Pius VII
But then in 1822 the Holy Office, issued another decree, actually applying penalties for not allowing the publication of books presenting the heliocentric solar system ‘according to the common opinion of modern astronomers.’
I will comment on tyhe Diamond Brothers denial of infallibility soon.
‘The most excellent [Holy Office] have decreed that there must be no denial, by the present or by future Masters of the Sacred Apostolic Palace, of permission to print and to publish works which treat of the mobility of the Earth and of the immobility of the sun [the defined heresy in 1616],
according to the common opinion of modern astronomers, as long as there are no other contrary indications, on the basis of the decrees of the Sacred Congregation of the Index of 1757 and of this Supreme [Holy Office] of 1820; and that those who would show themselves to be reluctant or would disobey, should be forced under punishments at the choice of [this] Sacred Congregation, with derogation of [their] claimed privileges, where necessary.’
Now why do you think decrees of a pope
would always put in the phrase according to the common opinion of modern astronomers? Because the decree of 1616, the infallible one, could not be touched as promised by Christ's Church. And the ploy worked. But as the Lord said;
For there is not any thing secret that shall not be made manifest
nor hidden, that shall not be known and come abroad. (Luke: 8:17)