How would we classify it when an adult developed a neurocognitive disorder leading to learning disability?

Quote from DSM-5:

C. Onset of intellectual and adaptive deficits during the developmental period
(Page 33: Diagnostic criteria for Intellectual Disability [Intellectual Development Disorder]).

[…] In acquired forms, the onset may be abrupt following an illness such as meningitis or encephalitis or head trauma occurring during the developmental period.
(Page 38: Development and Course)