Did you fire it up and look at the diodes? I wouldn't read anything into the the thicker conformal coating; I would count that as a plus, actually. If there all Samsung LM301B or whatever; all of them are pretty much going to look the same, as they all come off the same assembly lines. duh.
Looks like those sf and mar's logo's are printed on there by samsung, (that's kind of interesting), by the looks of it. Bottom line, all those LM301B diodes are exactly the same, doesn't matter if they were made last year, or today. It's the same design spec, so what really matters here is the warranty coverage. How long, and how reliable...
I can testify that I've had a burnt out sf light, and had zero problems with return. Easy response; although the support was overseas, but seemed professional. In fact; I wasn't even asked for the burnt light back, just actual proof that it went caput. I was admittedly somewhat responsible, and they still replaced it. So I don't get what your trying to imply here. Maybe a bit on the paranoid side today?
I get that way too sometimes.