It is officially announced that, in accordance with the settled general rule that a wife takes the status of her husband, Lady Elizabeth Bowes-Lyon on her marriage has become Her Royal Highness the Duchess of York, with the status of a Princess.
Times of April 28, 1923
I did not say that Queen Mum was not a princess at all. I wanted to emphasize here the difference between a princess by birth and in her own right (and style) and a princess by marriage only, who takes her status, title and style from her husband (and in the UK is even styled a Princess plus her husband's name). The first one was, for example, Queen Mary, born Princess Mary of Teck, and the second one (and first in history since Catherine Parr, the sixth and final wife of Henry VIII) was Queen Mum, born a commoner styled Lady Elizabeth Bowes-Lyon. Queen Elizabeth the Queen Mother was a Princess of the UK by marriage styled as The Princess Albert not Princess Elizabeth but under her daughter's will and according to old customs, she was styled like that at her funeral. It was because, first, her precedessors were all styled like that and second, her sisters-in law (except the Duchess of Windsor) were given the personal princely style by EII too.
I believe The Letters Patent of 1917 were completely personal to George V. His grandchildren would be Princes and Princesses throughout his lifetime and theirs, as is the case now. His great affection of the Princess Elizabeth was obvious. He probable felt that he would never see female line great grandchildren. He was correcting the orders of QV, who basically made everyone she was related to, or would make all of her decendents Princes or Princesses no matter how far they would now be from the sovereign.
Before the Letters Patent of 1917, male-line great-grandchildren of a Sovereign were also Princes and Princesses of the UK by birth but with the lesser style of Highness. Thus, the only child of Prince Arthur of Connaught, a grandson of Victoria through her son Arthur, Duke of Connaught, Alastair, was styled His Highness Prince Alastair of Connaught since his birth until the said Letters Patent of 1917 stripped him of that status and he become a commoner by law known as Earl of Macduff. Actually, he was the only member of the immediate Royal Family who was affected this way by George V's changes. Of course, there were the Hanoverian royal relatives of the King, far more descended in male-line from George III than Alastair was from Victoria, who were recognised with their titles of Princes and Princesses of Great Britain and Ireland (not the UK) by the King several years before he revoked it all by limiting the princely titles and status in his Letters Patent of 1917.
Until 1917 additionally male-line great-grandchildren were British princes and princesses by birth, so it's not like you said that Victoria wanted everyone descended from her to be British princes and princesses. It's true she was elevating her relatives in their styles, like her Battenberg female-line grandchildren, who were raised in the UK from their German
Serne Highness to
Highness, but they were never considered Princes of Blood Royal of the UK.