When several pipelines assemble instructions for the same downstream LLM generator, guidance added to one pipeline's prompt literal silently never reaches the others — even when a shared-fragment module already exists. Audit siblings by grepping fragment usage sites; promote rules to the shared module.
Diagnosed a production defect in a system where four pipelines (news-digest companion, growth/SEO, creator-scout, and direct user requests) all assemble natural-language instructions for one downstream LLM calculator generator.
The scout pipeline's prompt contained a hard-won framing rule: when a comparison is lopsided (the verdict would never flip), reframe from a neutral "Should I choose X or Y?" into "How much would you save with X over Y?" with a dollar output. A news-digest-generated artifact shipped with exactly the defect this rule prevents — because the rule lived only in the scout's prompt literal.
The kicker: a shared prompt-fragment module (TONE_RULES, FORMULA_RULES constants) already existed and was imported by all the assembly sites. The sharing infrastructure was there; the discipline of promoting new rules into it wasn't. The framing rule was written directly into one pipeline's string literal and stranded there.
Related findings from the same root-cause session:
Soft limits in prompts don't hold. "Labels should be <20 characters ideally" produced 20-21 char labels that wrapped a two-column results UI. Measured the actual UI break point (17 fits, 20 wraps), converted to a hard MUST with an explicit cap and GOOD/BAD examples.
Literal directives get literal compliance. "Use concrete numbers from the story as defaults" made the model copy 58143.34 verbatim as an input default. The fix distinguishes destinations: defaults get rounded clean values (58000); exact source figures belong in prose content where precise quoting is good attribution. When a directive says "use the source's numbers", say where each fidelity level applies.
Transferable practice: when you add any behavioral rule to one pipeline's LLM instructions, grep for the other assembly sites (search for imports/usages of your shared fragments — those are the sites) and either promote the rule into the shared module or consciously record why it's pipeline-specific. Prompt literals are code duplication with no compiler to catch the drift.