Possibly she fibbed about her age to avoid having her father's permission, being under age
That was my first thought too, seeing as to how they paid for a licence for a speedy wedding that dispensed with the calling of Banns in the church and possible objections from her father or any other person present,
But the marriage witnesses in the church were Wm Ed Brock and M J Brock (her father was William Edward Brock) so either the witness was father or a brother named after him and t
here was family knowledge and support.
The Licence was for Arthur George Pope & Dorothy Brock,
both Full Age. Wording includes
"And we being willing and that these your desires may the more speedily obtain a due effect, and to the end thereof that the Marriage may be publically and lawfully solemized in the Parish Church of Stoke Damarel, Devon, without the publication of Banns. ...Provided always, that if in this case there shall hereafter appear any fraud suggested to us, or truth suppressed at the time of obtaining this Licence, then the Licence is Void, and of no effect in Law, as if the same had never been granted and in that case we inhibit all Ministers, if anything of the premises shall come to their knowledge, that they do not proceed to the solemization of the said Marriage, without consulting us or our Vicar GeneralValid for 3 months. Dated 5 March 1919, married 8 March 1919 so only 3 days later.
The Licence was presumably desired as the groom Arthur George Pope was a Private R.M.L.I Royal Marine Light Infantry onboard HMS Carnarvon and likely had only a few days shore leave.
Arthur George Pope, Service number 13994, born 14 April 1893, served on the Carnarvon from 8 Oct 1918 to 25 Aug 1919 (possibly up to the point it became a training ship which was sometime in 1919 - wikipedia). He continued in service in Plymouth Division and onboard a couple of ships till 13 April 1932, having enlisted 21 Mar 1908 in London, being underage for the 1st 3 years. The date of Marriage Plymouth 8 March 1919 is on his Service Record at the top, incorrectly at bottom as When married: 8 March 1917.
https://findmypast.co.uk/transcript?id=GBM/ADM159/44771They married after the end of WW1 (Armistice Day 11 November 1918) but before the Treaty of Versailles 28 June 1919.
Most people didn't keep their marriage Licences, is superceeded by the marriage cert.
There may be another copy in the Archives of the Diocese of Exeter
https://devon-cat.swheritage.org.uk/records/DEXolder ones are deposited
https://devon-cat.swheritage.org.uk/records/DEX/7/a some may still be at the Diocesan Archives at Exeter Cathedral. Registers of Licences issued were maintained just as Parish churches kept Registers of Banns, some of which we can see online pre-1837 and during civil-registration.
The Church bound Marriage Register is viewable on Findmypast
https://findmypast.co.uk/transcript?id=GBPRS/M/35279008/1 and has the bride and groom's + witnesses'
signatures2 books kept one for the church, the other for Devonport GRO (deposited with them when full); both signed on the day.
Devonport abolished 1937, becoming Plymouth
https://ukbmd.org.uk/reg/districts/devonport.htmlYours does not have signatures as is an official copy made by the minister on the same day for the Bride & Groom as they paid for a paper cert. [If you ordered a copy from the GRO in Southport today via www,gro,gov,uk that would be of the later quarterly copies made and returned by the minister S G Ponsonby for the period 1st Jan -31st March 1919 ie all his handwriting. If you instead ordered a marriage cert from the local District, Plymouth Registrar's Office that would show the signatures IF they have the ability to scan & print from their now fully filled book, or could just be typewritten, just as valid legally]
Why did she need to say Full age and 21 if was 19 and had father's/family approval can't think of a good reason. Perhaps the Bishop assumed, we don't know who gave the info one, or other or both, but as the Licence was for 2 people of
Full age they wouldn't have want to highlight and correct it on the 8 March as the Vicar might not have proceeded. After the marriage (whether by Licence or Banns) if someone of Full age turns out to be actually a minor it does not make the marriage void [many married by Banns underage in churches distant from their family home with a congregation of strangers unlikely to object and perhaps father totally unaware].
AnthonyMMM may have opinion if he happens to read your post.