I don't think Mountbatten-Windsor is her surname. https://www.msn.com/en-za/entertainment/celebrity/birth-certificate...
If the birth certificate in Prince Archie Harrison Mountbatten-Windsor's profile is legitimate, the "Mountbatten-Windsor" can definitively be pulled from Meghan's name fields.
Antonya Angelika Bryony Cooper is talking about https://www.geni.com/documents/view?doc_id=6000000093518163024&, which is titled "Baptismo." I've corrected the title.
Allow this to clear up all misunderstandings:
"The Royal Family name of Windsor was confirmed by The Queen after her accession in 1952. However, in 1960, The Queen and The Duke of Edinburgh decided that they would like their own direct descendants to be distinguished from the rest of the Royal Family (without changing the name of the Royal House), as Windsor is the surname used by all the male and unmarried female descendants of George V. It was therefore declared in the Privy Council that The Queen's descendants, other than those with the style of Royal Highness and the title of Prince/Princess, or female descendants who marry, would carry the name of Mountbatten-Windsor."
-The official Royal website.
Also this article from when William & Catherine married:
"Now that Prince William and Kate Middleton are married, some are wondering their last name.
Like other descendants of Queen Elizabeth II and Prince Philip, William's surname is Mountbatten-Windsor, and it will be Kate's too by marriage.
As explained by the official British royal website, the Queen's descendants carry the royal surname Windsor, as well as the name Mountbatten to reflect her husband Prince Philip's surname.
The royal website explains further that the surnames are not always used, only when they are formally needed, such as the case of marriage.
While Prince William will be recorded as a Mountbatten-Windsor in the marriage registry today, he may choose a new name at a later point, specifically if and when he becomes king. As explained here, "Since a royal proclamation is not binding on succeeding rulers, King William could decide to add a name or two."
Prince William and Kate, who will go by the name of Catherine, also gained the titles Duke and Duchess of Cambridge upon their marriage today, conferred upon them by Queen Elizabeth II."
"A Guide to Royal Family Titles, from the Queen's Specific Styling to Prince Harry's Scottish Moniker" by Chloe Foussianes on May 10, 2019 in Town & Country Magazine:
https://www.townandcountrymag.com/society/tradition/g26783028/briti...
List of "Proclamations, Letters Patent and Warrants", 1917-1999, with dates and descriptions for further read (unfortunately links does not work).
http://cuhags.soc.srcf.net/info/proclp-w.html