Datapoint Manx English/Relativizer that or what in non-restrictive contexts

Variety: Manx English
Feature: Relativizer that or what in non-restrictive contexts
Value: C - feature exists, but is extremely rare
Informants: Jennifer Kewley Draskau

Examples

Example 1969:
Ould Anthony Lee, that might have knew better

Source: Brown 1936: 137