Impossible to say because there are so few examples seen. I know of only the two in this thread. With a sample size of n=2, it is impossible to draw conclusions on minor piece-part changes that may or may not be original to either of the guns in question. This is why I'm still fairly skeptical on your '50 spike bayo, there is only the single example and all other "EM" prefixed guns have been shown to be '49s or at least have '49 receiver covers. The smooth takedown lever on your buddy's gun is certainly neat but is it indicative of early '49s, mid 49's, late 49s, or was it a part that slipped through QC somehow? Maybe bubba exporter Kyber Pass'd one up and installed it to be able to sell the gun? Impossible to say without seeing other examples on other guns, establishing the pattern and then finally making the determination. This is what we did with the external rivet on the early '49 magazines. Justin Hell made the initial observation, we followed up with a deep dive through the data, had quite a bit of discussion, determined that certain 49's had the feature and others didn't, then associated S/N blocks to the guns that did and could finally piece together the story reasonably well that it was an early feature that was quickly transitioned in mid-49. Absent a primary source who acquires this info from firsthand knowledge (documents, blueprints, museum pieces, interviews with technicians who built them, etc.) that's the best we're ever going to be able to do.
We can look at the two 48's and see that the two gas tube takedown levers are quite different from the SKS45s that went into production as are the two bayo collars, the receiver cover text, the two receiver cutouts for ejected shells, etc. Beyond simple 10,000 ft view stuff like that, it's really quite impossible to say much more at the component level in detail with any degree of certainty. As with the "ex-DDR" internet gospel floating around out there that refuses to go away, I think it would be a great disservice to the SKS community to assume we or anyone in the SKS community could concretely identify all or even most of the changes on these '48s with random photos of just two different guns.