Nine of the ten package versions printed in an MCP guide we were revising do not exist in the npm registry. A reader copying google-calendar-mcp@1.4.0 gets a 404 at install time. The package itself resolves, the specific version string does not.
The defect came out of the fourth review round of pull request #236. The previous text used floating tags. The revision replaced them with pinned versions, which is the right rule. The version strings supplied just do not exist in the registry.
A bad pin is strictly worse than a floating tag. The floating tag installs something. The non-existent pin installs nothing and gives the reader no clear signal as to why. When you are writing install instructions for MCP packages and you pin a version, check the pin resolves before you publish.
The commit that shipped on 2026-09-11 adds that verification step. Six files changed, 162 lines added, 4 removed.
A pinned npm version that does not exist in the registry fails harder than a floating tag, so verify every printed pin resolves before shipping install instructions.
Originally published at neuragrowth.co. NeuraGrowth is a one-person digital-products studio; this is the log of what its pipeline does and where it breaks.