IDK. When a mfr says, “Be sure to give beers made with XYZ yeast a sufficient diacetyl rest.” I tend to believe them and give it a day or two at 65°F or so to rest.
I guess I could take a hydrometer sample and taste test it. …but a day or two doesn’t hurt one way or the other IMO so I let it rest in those cases.
My last lager, made with diamond, tasted it great on day 8. I decided to keg. A week later it was a diacetyl bomb. It’s been sitting upstairs ever since. Hopefully, time will fix it.
i had the exact same thing with diamond lager on the first beer i used with it, second beer (just checked my notes since it was from a year ago) i warmed up after 5 or 6 days to mid 60s and no diacetyl.
im not going to explicitly say it, but lol some people will always disagree with certain brewing opinions and in the end you simply have to choose what you go with and what you dont.
i think a factor re: the value of a d-rest or not and diacetyls existence in the finished and packaged beer that explains why some people don't believe in it could be having strong temperature control during fermentation AND very stable temperature to store the packaged beer. somewhat related but re: hop creep's existence or not - a similar thing, i was listening to vinnie cilurzo discuss his battles with hop creep (heh - indicator - it does exist!) and that the enzymes that cause it are not active if the beer is stored in the 50s or lower after packaging. my beer ends up needing to be in the 60s to bottle condition and often ends up all the way up to the low 70s by june let alone july.
these things like hop creep or the value of a d-rest, which are widely noticed and discussed do exist, but may be absent or heavily mitigated dependent on a ton of individual's factors.
and to clarify the diamond beer i had the issue with, i distinctly remember tasting it on bottling day and noting "wow this is so aromatic, pleasant and flawless." then 10 days later yeah, completely different flavour with flaw.