Also of note, not all the SMLE's were leftovers from WWI as you stated. Production had continued in spurts throughout the 20's and 30's, and I believe some factories continued production into WWII, since there was no tooling available for making No.4's until later in 1940 or very early 1941. Those 'obsolete' rifles you're complaining about could very well have been fresh off the assembly line.
And the rear sight on a No 1 is pretty robust. The armourers would not only have likely had proper spare parts, since both rifles were in widespread service, but I'm guessing there were some spare rifles kicking around at the time.
Not complaining about the Mk.III at all, I have one myself and very much like the rifle, I wonder were that came from, anyhow, my observation as recorded at the outset when I started this post was how
regular infantry units fighting on the front lines (note in bold) and not as mentioned previously repeatedly,
rear echelon and non front line troops like support troops are still issued Mk.III's with cutoffs and volley sights.
My OP was just a observation that came from my previous 12 years of army service which also comprised time in brigade EME units that actually carried out the function of supporting and repairing issued infantry weapons, that these pictures seems to contradict normal modern battlefield infantry small arms doctrine. And that by 1941 and 1942 these front line infantry should have the updated Mk.III* at the least and most definitely not the Mk.III with mag cutoff and volley sights.
The British military found early into WW1 that the mag cutoff on the Mk.III was a tactical problem for 2 reasons, one was that it slowed down the loading of the rifle in the heat of battle as soldiers trying to load their mags with clips sometimes failed to notice that the cutoff was on and blocking the mag, especially during the night and in dim smoke filled areas or when under battlefield stress. It also slowed down the loading in battle when they had to disconnect the cutoff.
Also, they had it removed when they found that the new trained method of rapid fire by using your palm to cycle the bolt during advancing rapid fire was impacted by soldiers hitting their palms during the forward movement on the cutoff which slowed the movement down and sometimes activating the cut off.
It was a obsolete rifle feature from a time when the military had just progressed from single shot rifles and did not need or want their soldiers using rapid fire at will as the soldiers were trained then to only fire on each instance as commanded/directed by a supervising officer. This tactic went out well before WW1 and was never brought over to the P14 as a needed feature when it was designed in 1913.
I will leave it at that as I think this post has gone way off tangent and have no desire to debate further the reasons why they still had front line infantry with mag cutoffs and volley sights when by 1941 the British had by reliable estimates already 4 million No.1 Mk.III*'s from WW1 and 1.5 million No.4 Mk.1's with a standing army of only 2.2 million men in all fields including cooks.
So why they had front line infantry using Mk.III's with mag cutoff's and volley sights in 1941-2 and maybe later is baffling when you would think they could have just issued all the updated rifles to the infantry as they moved to the front and left the older rifles for the supporting troops.