They are close, @Formidilosus has pointed out that the eld-x has a small space in the nose between the copper and tip that doesn’t have lead in it, where the eldm can be filled with lead completely. He pointed out that this has caused issues with the eldm (rarely though) and it has been more prevalent in certain calibers and grain weights. I can’t recall exactly where it was said and shown. I believe it was in one of the new heavy TMK threads.I think they’re functionally basically the same bullet, at least subject to the same manufacturing variations and resultant variation on target which is more important than their minor construction differences.
I’m certain every maker has lot to lot variation, it just seems like Hornady’s variations show up in animals more. And I say that as someone who shoots Hornady bullets more than any other maker by a large margin and have hunted with interlocks and SSTs and interbonds and eldx and eldm and SST-ml and Vmaxes.