What are the primary-sourced founding dates, enrollment figures, and educational mechanism for the emergence of Nicaraguan Sign Language?

The account that Nicaraguan Sign Language (NSL) emerged in Managua special-education schools that opened around 1977 and expanded through the early Sandinista period — after a spoken-Spanish/lipreading (oralist) curriculum failed and the deaf children built a shared gesture system among themselves in schoolyards, streets, and buses — currently rests in the vault only on Wikipedia (Tier 4). See claim-nsl-emerged-in-managua-schools-after-failed-oral-spanish-curriculum, which carries an [unverified-quant/mechanism — needs primary] flag on the dates, enrollment numbers, and the causal "oralism failed → children created a system" mechanism.

Why it matters

The founding setting is the causal setup for the vault's two well-sourced NSL claims (language from zero exposure and the cohort effect). Dates, enrollment counts, and the specific role of the failed oralist curriculum are exactly the kind of quantitative/mechanistic detail that journalism and encyclopedias garble, and they should not go load-bearing on a Tier 4 source.

What would answer it

• A primary Judy Kegl source (e.g. Kegl, Senghas & Coppola 1999, "Creation through contact: Sign language emergence and sign language change in Nicaragua," in Michel DeGraff, ed., Language Creation and Language Change) or Senghas's own dissertation/papers, read directly for the school founding dates (the two relevant schools and their opening years), enrollment figures, and the documented account of the oralist curriculum and how the shared system arose.
• Cross-check the specific years and numbers against at least one Tier 1–2 source before promoting the flagged note past seedling.

Candidate next moves

Pull the Kegl/Senghas/Coppola 1999 chapter or Senghas's MIT dissertation; if paywalled, look for an author-hosted PDF or an archived copy. Trace which of the two Managua schools (the initial primary school vs. the later vocational center/adolescent program) each date and figure belongs to.