Non-standard standards...
Four wall boxes today: three Elizabeth II boxes, one George V. All show variations: their border design, or their height, or the placement of their cypher / collection-plate. Compare post 1 GV wall boxes, with the one on this post: they all differ.
The EIIR box with its cypher at top is, I believe, a later
Ludlow design wood carcass wall box. Its frame is wood. It is similar (with very minor differences) to an example in Dorset.
If you like hunting for distinctive, rare or old post boxes, then the
Letter Box Study Group can help. Full information is only available to paid-up members - however, free-to-view photos are on the below links:
Wall Boxes. Below are a selection of photographs contributed by members of the Group.
lbsg.org
Pillar Boxes. Below are a selection of photographs contributed by members of the Group.
lbsg.org
I'm not a member - my interest is just casual fun - and I use a different way to "hunt" unusual and interesting local boxes:
I1) I choose an area of a few square miles,
2) I find the postcode for a business within that area,
3) I enter the postcode on Royal Mail, here:
https://www.royalmail.com/services-near-you#/
4) Royal Mail's web page then shows all its active post boxes in that area.
5) I open Google Maps (in street view) and I I go - virtually - to each location, to see what the box is. It's a bit laborious but it means I can find boxes worthy of visiting in person.