But generally, I'd say the e30 is neutral/warm yet detailed with a pleasing full bodied sound. It's 'hi-fidelity' in the sense that it imparts virtually no sound signature/sound stamp of its own onto your music collection.
The barrels are numbered. Whether that is a serial/production/batch number is unknown. the ranges of those in my possession range from M103 to m305. .
One set (M103 printed on the barrel), has a smooth cable whereas the other 4 sets have a braided cable. The smooth cable is from earlier in the production run from what I can gather and it sounds excellent.
Whether the sound differences are from intentional production changes over time, from uncontrolled production variation, or from differing burn-in times is unknown but I'd wager it's a result of the last 2 phenomena.