So I know that identical RAM from different sets / kits may cause system instability. I'm talking about RAM with identical brand & serial numbers but with a different batch number (usually a 4 digit number).
I've had first hand experience with this issue with regular non ECC RAM - but my question is if that's true for ECC Registered RAM?
I'm looking at RAM on eBay, and one of the sellers is telling me that mixing identical sets this is not a problem with ECC Registered RAM - so just want to clarify it.
Also, not sure if AMD vs. Intel platform makes a difference in this case, but I'd be using this with AMD.
DIMMs with the exact product no./SKU are usually compatible between different batches - from most vendors, especially the big ones.
The kind of memory in that SKU - unbuffered, registered, LR - doesn't matter. You need to make sure that new memory is compatible with what you've already got installed, either by spec sheets or vendor support.
Sometimes you can mix (slightly) different memory (e.g. different chip sizes) in different channels or across CPU sockets but again, that depends on the actual hardware at hand.