Guidelines look great in a PDF and collapse in a 1:1 ad frame. Design the hostile placements first.
Every identity looks convincing at 2000 pixels wide with generous whitespace. The real test is a six-second vertical video, a favicon, a dense dashboard table, and a paid social frame competing with a thousand others.
So design those first. Establish the smallest, fastest, most constrained expression of the brand, and let the expansive stuff follow from it. A system built from its hardest case scales upward easily; the reverse almost never works.
Ship the system as code, not as a document. Tokens, components, real examples. If producing on-brand work is slower than producing off-brand work, the system will lose.