Use of AKM assault rifle during the Soviet-Afghan war
This article about the history of small arms during the Soviet-Afghan war mostly has it roots in the early day of Soviet-Afghan war reenactment.
Problem with AKM on reenactment events
Reenactment events depicting Soviet-Afghan war started to take place in mid 2000s, when the development of the internet was still at it early stages and so the information on this war was limited. The logic for AKM was very simple at the time - if the AK-74 was only adopted in 1974, it is not possible that the whole army was armed with it by 1979 and even during the Soviet-Afghan war.
On top of that, the gear available for purchase was also limited to just couple of airsoft producers. Hence, in late 2000s and early 2010s it was not unusual to see Soviet side on an event armed primarily with AKM or AKMS guns. AK-74 and AKS-74 at the time were limited in numbers and usually of poor quality, so their airsoft capabilities were unsatisfactory for most buyers.
All in all, at the time, the AKM was usually dominating the battlefields of the airsoft Soviet-Afghan war. And, of course, as we know now, this was pretty farb.
The real use of AKM rifles in Soviet-Afghan war
Of course, the 7.62 AK variants were used by the Soviet troops in Afghanistan. There is no point to deny that.
However, they were used in extremely limited numbers. We are talking about one per a platoon or so. Their primary use was as a silenced weapon - with PBS-1 silencer attached and using subsonic ammunition. The battle order for this type of weapon is unclear. It is believed, that they were supposed to belong to the recon companies and battalions of the corresponding units, but it would not be unusual to see AKM and AKMS rifles on photos from the regular infantry and airborne battalions. It is most likely, that these silenced weapons belonged to the bigger unit and were issued on a mission per requirement.
What is interesting, is that the PBS-1 has a very limited lifespan. The rubber insights have to be changed regularly (they come in ammo crates together with the subsonic ammunition 57-N-231Y). Because of that, some 7.62 rifles were used without the PBS-1 silencer in the later years of the war.
Also, there is an exception for mass use of AKM rifles. This is to reenact the very first month of the war, when the mobilized infantrymen from 5th and 108th Divisions were called up to invade the Afghanistan. Though, for some reason, this impression is not very common.
That one unit which only used AKM throughout the Soviet-Afghan war
This is a lesser known fact, but there was one unit that refused to use new AK-74 rifles and carried on with the time tested 7.62. This was the 781th Independent Recon Battalion of the 108th Motor Rifle Division.
According to the famous book "Afghan. Bagram. Reconnaissance", the 40th Army command was forcing all the units to adapt 5.45 weapons as soon as possible. But the officers of the 781th battalion used somewhat arguable argument that 5.45 rounds ricochet from the branches and leaves. I am not gonna ask how much green zone there is in Afghanistan and how true is the claim itself. Neither did the head of armament of the 40th Army and the battalion was allowed to keep the 7.62 AKMS rifles as their main weapon.
However, for some reason, the battalion did adapt 5.45 RPKS-74 machine guns instead of the old 7.62 ones. This is both mentioned in the book and can be seen on the photos.
The story with this unit using 7.62x39 en-masse ends sometime between 1984 and 1985. At this point they were forced to rearm and been using regular AKS-74 rifles ever since. The possible explanation is that the AKMS rifles that they have used wore worn off at this point and did not provide acceptable accuracy. Since the Soviet Army was mainly armed with 5.45 weapons at this point, it was too complicated for the logistics to make an exception for them.
Correct historical solution to use of AKM
If you want to use the AKM correctly for your Soviet impression for the Soviet-Afghan war, you pretty much have to do everything right. And the first thing is to choose the exact unit you want to make impression of. All the way down to the company size, preferably.
The important, yet counterintuitive thing to remember is that the airborne units, such as the 56th DShB had mainly wooden stock AKM rifles. And so did most of the infantry units. VDV guys from 103th division used folding stock AKMS, but 345th airborne regiment, again, used full stock AKM. The logic behind this is unclear so I can't reliably comment on it. My theory is that the independent brigades and regiments were on an infantry line of supply, so the divisions which were helping them out simply didn't have any folding stock rifles to hand out.
The Spetsnaz used the mixture of both, but mainly folding stock AKMS. And again, it all depends on the exact SpN unit. So choose carefully what you want to reenact and buy a rifle accordingly.
All in all, if you are on your own and using an AKM or AKMS - it is not farb in any way. It can always be justified, with or without PBS-1 silencer. However, when you get into a team, it is very advisable to limit the number of AKMs to 1 per 10 people or so. Given that most teams do not grow beyond the size of 5, having one AKM per group is a way to go.