This cutting from the Sept 1986 S25 justification document mentions a new generic name being proposed to the International Bureau Of Standardization Of Man-Made Fibres. I guess this was tencel. (Comments from those involved would be welcome).
Between BISFA considering tencel and Courtaulds later adopting Tencel as the brand, two or three years elapsed and lyocell was chosen as the generic because tencel had become too associated with the Courtaulds fibre.
(FIC = Federal Trade Commission?)