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In my experience FPIA in green ink is a name amendment (for reason other than marriage) and I believe LND is the district code for London where the change was made/originated from  The original district codes for some London boroughs would no longer be applicable following the establishment of Greater London in the 60's. There is a similar example further down the same page as your subject.

I just noticed that it's not the same car in pictures 2 & 3.  Bonnet shape and headlights....  A better scan of the car and left hand building/people in image 1 would be useful.

A timeline of relevant news snippets and other information that I've noted for the period 1912-1924

04 Jun 1912 Davidson the Bishops Cannings trainer has taken the stables and gallops at Woodyates and is expected there shortly

13 Mar 1913 Tuesdays training... Whitsbury, Toyd & Woodyates .... Davidsons Limerock, Little Madge, and others covered 5f
12 Aug 1913 Folkstone race 1:30 5f 1st Mr R Jeffreys Little Madge... Winner trained by Davidson
16 Sep 1913 Warwick race 3:00 6 furlongs 1st Mr R Jeffreys Dark Simon... Winner trained by Davidson

02 Oct 1914 Newmarket race 2:30 1mile 1furlong 1st Mr G Edwardes Drinmore... Winner trained by P Hartigan at Ogbourne

   Apr 1915 J F A Davidson attached to RND 1st Brigade Hd. Qtrs Blandford. Next of Kin, Wife H L Davidson, The Rowans, New Church Rd, Hove

23 Feb 1917 Death Davidson, Feb 14th at Fairfield Rd, Blandford Hilda Louise, wife of J F Davidson RND of Woodyates, Handley

20 May 1919 J F A Davidson demobilised at Crystal Palace
   2Q  1919 Marriage John F St A Davidson m. Grace Mabel Nailard (first wifes sister!) Steyning, Sussex

18 Mar 1921 Trainer Pat Hartigan dies at Liverpool falling out of hotel window on grand national eve!
22 Mar 1921 Female Davidson Premature birth and death at 'The Box, Maizey, Ogbourne St. Andrew' Father & informant John Francis St Alban Davidson present at death
24 Mar 1921 Large number of horses still at Ogbourne... kept in work by J F Davidson assistant to the late trainer Pat Hartigan
28 Mar 1921 J Davidson formerly trained at Bishops Cannings has been acting secretary to late Pat Hartigan has received his license to train and will take over the charge of the Ogbourne horses
16 Jul 1921 Davidson who was poor Pat Hartigans secretary, and is now training at Ogbourne is the son of a clergyman...

31 Jan 1922 Mr R Crawford the trainer has arrived at Ogbourne to take the place of Davidson who left yesterday for Collingbourne
14 Jul 1922 T Ellis charged with stealing bottle of whisky belonging to J F Davidson at Salisbury race course 6 Jul. Goliath Black, chauffeur of Collingbourne Ducis and employed by Mr J F Davidson.....

   1Q  1924 Birth John A Davidson. Pewsey, Dorset mmn. Nailard    
28 Nov 1924 Cook wanted.... also Nursemaid for boy of ten months....Davidson, Herridge, Collingbourne, Wilts

I haven't found the definitive date that Davidson became Hartigans assistant but I suspect its c1913.

Edit: Forgot to add image of the winning horse mentioned 12 Aug 1913...

I think the garden wall and brick detailing on the central chimney clinches it. And... Hildas Sister gives her address as New Church St Hove when registering Hildas death.

Looking at the original image https://images.findagrave.com/photos/2015/131/146391802_1431468752.jpg, I think the top part reads: