ignore sugar leave trichomes.
only scope and concern yourself with the trichomes on the buds.
General consensus (anecdotal only) is 10-70%? 20-80%? amber (google searches of similar sites like this and word of mouth)... there is a big window there to explore. I'd suggest trying early-middle-and-late harvests and personal opinion will guide you in the future.
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Some die by amber, some do not... find out what you prefer.
The fact most of it is based upon, but not necessarily extrapolated accurately from: Amber means the delta-9-THCa has degradated to a less psycoactive or maybe less-preferred psychoactive molecule. CBA? doesn't matter what it is.. it is no longer what we want.
Some amber is likely optimal, but anyone confident about a specific % is lying to themselves and just following the herd of others using non-scienctific data. I know what i like, but i am not confident it is 'optimal'. Maybe, there's more to it than just THC% too, etc etc.
If you asked farmers if they were doing anything wrong in the decades leading up to the dust bowl, a man-made catastrophe definitely caused by poor farming techniques, they'd call you stupid and likely be belligerent or violent toward you. It is more like a religion than science - just what people do often for no reason. even though they were the ignorant ones in hindsight. Be wary of extrapolations that are followed like a religion but lack the data to support it fully.
In this case, there is something behind it, at least... the degradation spoken about does occur. you can see THCa 'fading' to some extent on the surface via amber color. The extrapolations after that are a bit suspect, though, even if they end up being correct.. it'll be a little luck involved as it is a bit of a blind stab in the dark with incomplete information.