A plant can be full of detailed, correct work instructions and still have zero actual Standard Work — because writing down "how" isn't the same activity as establishing "at what pace, in what order, with how much inventory in motion."
These two terms get flattened into synonyms constantly, and it leads plants to believe they've achieved lean flow when they've only documented tasks. A work instruction is a narrow, task-level document — the detailed step-by-step "how-to" for performing one specific operation correctly, like a torque sequence for a bolt pattern or the assembly steps for one sub-component. Standard Work is a broader, system-level lean manufacturing concept: it combines takt time, the standard work sequence, and standard WIP together for an entire process. Work instructions can plug into individual steps of that sequence as supporting detail — but they are not a substitute for the other two elements, and never were.