Ok...maybe not as qualified as a Dell driver but I've built well over 10,000 PCs and servers, some of which have been or still are in use in some of the most adverse environments in the world, from the top of mountains to military installations. I've seen hundreds of memory-related issues when types have been mixed. The bottom line is if you mix memory you "could" get issues, even today. I'm not saying you will though - there is an important distinction. More fool you if you dispute that.
Define professional? A Dell RTB courier doesn’t quite fit the description. Mixed RAM specs is more likely to cause an issue as it’s using what happened to be laying around. Probably an old poorly stored sore stick or pulled from an inoperable carcass. Even then it’s probably the additional stick might not officially be on the QVL list. Last year Ryzen showed that memory can be finicky. However that was due to poor initial BIOS revisions, not due to the JEDEC standards and protocols.
Does anyone ever buy direct from Crucial? I use it to check I'm ordering the correct RAM.
Picked one up today was hynix 😣
cheers need to get myself some memory :)