Most Tamil dialects, by contrast, retain in both the spoken and the written languages a well-developed system of person and number verb agreement morphology.
With Karnataka based Saraswat Konkani (Nadkarni 1975), Tamil Nadu based Saurashtri (Smith 1978), Sri Lankan Creole Portuguese and the Urdu, Marathi, and Kannada dialects of Kupwar (Gumperz and Wilson 1971), NFT grammar is the outcome of pervasive structural realignment as a result of stable bilingualism.
This would suggest that the Negombo dialect continued to evolve in the Coromandel Coast before it arrived in Sri Lanka and began to get influenced by Sinhala.
[3] Steven Bonta Negombo Fishermen's Tamil (NFT): A Sinhala Influenced Dialect from a Bilingual Sri Lankan Community INTERNATIONAL JOURNAL OF DRAVIDIAN LINGUISTICS XXXVII (2) pp133–140.
Steven Bonta, Ph.D. 2004, "Negombo Fisherman's Tamil: A Case of Contact-Induced Language Change from Sri Lanka" Cornell University