I would say all four athletes, El G, Ngeny, Jakob and Nuguse could have produced these 3:43.xx times clean.
If we assumed a PED existed, for the elite men's world class performances in the 1500m/mile, that is powerful enough to produce significantly unnaturally fast times, and the use of this PED was and is widespread, especially during the "full-throttle era" when testing was non-existant, then statistically we should have seen many more athletes/performances, say within 4 seconds of El G's world records (i.e. sub-3:30 for 1500m and sub-3:47 for the mile).
In the 1500m, before the era of new shoes, only about 2 dozen athletes had run sub-3:30, about a dozen ran sub-3:29, and only 5 ran sub-3:28. These performances are more or less distributed evenly across the +/- 30 years since the era of Coe, Ovett, and Cram, with no obvious link to doping eras or anti-doping milestones.
This changed noticeably in recent years. Since the supershoes in the last 5 years, the number of 3:30.0 or better performances jumped from about 101 to 145 (today), or about 45%.
Nick Willis estimates that the new generation of spikes are worth some 2-3 seconds for the mile (he became a believer when he ran a 1200m time trial 2 seconds faster than expected.)