On paper at least, the 077 and 2405 have not had any changes and they should all perform the same whether an example of their earliest production in the mid '70s or the latest production in the early 2000s. Years ago I measured a number of
JBL's ring radiators and found a fair amount of unit to unit variation. Because the tolerances are so tight at these frequencies I imagine unit to unit variation was always an issue. On top of that this is compounded by age and possible years of misuse.
Within reason, I don't think a DCR variation will directly correlate to any audible differences. That said, if the goal was to have a perfect pair of 077s or 2405s I would want to gather a large sample group and carefully measure their responses. I would then pair them based on their measured FR and sensitivity. I wouldn't be at all concerned by their DCR measurements. I think this number is mentioned so often, because it is the only measurement most eBay sellers have available to them, not because it is of any particular importance.
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