Evan, to some this is Enfield minutia, but to me it is important to the detective work and helps satisfy my OCD!
Great question. I used to puzzle about this and still don't have a definitive answer.
At one time, I would try to make sure that all the parts that I put into a rebuild were the correct model, maker and inspection mark. I spent a great deal of time and energy searching for correct parts. But that is my hobby, the hunt is as much fun as the catch.
Then one day I picked up a very dirty long rifle, a 1892 Mk.II Metford I think it was.
I read the rifle. It was an Enfield, it had been back to the Birmingham Repair facility twice in its service life once in 1894 and once in 03 to have upgrades or repairs. While it was at the factory, it received a new nose cap and barrel band, the bolt head was changed out, the rear volley arm was changed along with its spring and it had a new mag fitted. The rear sight leaf was changed out and the new one renumbered. The front sight ramp had been slotted and a new insert pinned in place.
These were obvious to me, this Enfield made rifle had BSA parts on it. The patina on these parts looked newer than the action. The sighting had been upgraded, probably in 1903 following a directive correcting the sighting for bullet drift.
It then was cleaned up, serviced and shipped to New Zealand in 1914, where did service in WWI and maybe WWII. It was surplused and sold through the British Gun Trade in 1952 and then exported to Canada.
I rummaged through my parts bins for Enfield marked parts. I laid the parts out on the bench and sorted through looking for correct WD broad arrow marked to put on the rifle to correct it. Once I got everything mounted, I cleaned and admired my now improved rifle. It then dawned on me.
The next owner would pick this rifle up, and maybe see the tiny BR inspection markings and read that it had been back to Birmingham for repair at some time and that would be it. I had removed evidence of where this rifle had been and what had been done to it. For all this time I had been thinking that I was 'improving' my rifle when in fact I was destroying its history by removing the armourer fitted parts.
To tell the truth, if I now pick up a rifle and it has all matching livery parts. Every piece is marked as per the factory original rifle, it makes me suspicious. My first thoughts are not 'this rifle retains all its factory original parts', but more along the line of 'somebody has been messing with this one'.
A service rifle would be repaired and refitted by an armourer who did not pay attention to any brand or marking on a part in the bins. Parts is parts. Perhaps by chance he would fit a BSA part on a BSA rifle etc, but mainly by luck.
Saying that, I do try to fit a BSA bolt in a BSA receiver because the factory would have used the same set of gauges in manufacture. Maybe my imagination, but I find Enfield bolts fit best in Enfield receivers, Sparkbrook in Sparkbrook etc and so on.
The Birmingham Repair facility would refurbish rifles en mass. Batches would be mixed makers. Bad rifles would be stripped and parts recycled. The result was rifles rebuilt to as new specs, but total mixmasters.
Now when I read a rifle, these 'non matching' parts are part of the story and get my attention.
So to answer your question.

The date of change of stamp use has always been a bit staggered between factories. I guess that not every inspection department got the new stamps for the new new logo or new monarch at the same time. There can be a bit of a lag. For example, often seen are actions with a Victorian first proof and an Edwardian second proof.
The 'WD broad arrow' figure was introduced in 1855 and was used up until 1896 on subject rifles (later on bayonets and other equipment). It is a British Government Acceptance mark. An ownership mark if you like.
The EFD logo appeared in 1897, which is a RSAF Enfield factory logo, not a Government acceptance mark. You will find that EFD will be marked along with the broad arrow acceptance mark separately somewhere close by...eg, trigger has EFD one side, broad arrow on the other. This then morphed to EFD marking incorporating with a broad arrow above, and then later to EFD with an inspector number below and a separate broad arrow somewhere adjacent.
WD is an odd ball, I have seen parts marked with it on early Metfords (1889) and it seems to disappear around 1896 as factory inventory was used up. The jury is still out on this one, WD marked parts appear on all years of 90s rifles and carbines. But they could be replacements.
I need to find a copy of 'The Broad Arrow' by Clive Law. Lots of good info on markings in there. I lent my copy to somebody, but can't for the life of me remember who (who has my Dark Side of the Moon CD? Who has my valve compressor? Who borrowed my multi meter?)
More pertinent is what model of cut off should be fitted? Default to the type fitted to the sealed pattern arm. An EFD marked unit will be a version with the short taper on half of the front edge as opposed to the full width. ie. An Enfield cut off as opposed to a Metford one.
They both fit, they both work and neither would be 'incorrect' for an arm maintained in service.
Original from the factory, it would have been EFD marked, yes.