This study explores cross-generational variation in the effectuation of an English phonological contrast by bilingual Polish Americans in New York City. It asserts that the cross-generational evolution from global interference impact to focused transfer presence is filtered via L1 markedness and mirrors speakers' increasing reactivity to L2 phonology and social considerations. The discerned asymmetries in interference-transfer diffusion are inexplicable by extant models of L2 acquisition and inspire a perspective on L1/L2 phonetic categories as ruled by a variable grammar with admittance to phonological and social information.