Salaams All...
The reason why there is an apparent gap in the detail regarding Pre Portuguese and post Portuguese kastane making in Sri Lanka was because ....
according to
http://thakshana.nsf.ac.lk/pdf/VIDUR...%2019_1_30.pdf
Quote"In ancient times the caste system was mainly occupational based. As a result technology was preserved by being handed down from generation to generation.The caste system was developed to maintain the socio economic systems of the day.The social system changed with the advent of foreign rule and as a resulot the traditional technological know how was lost under colonialism.
Another reason for the decline was the cheap import of iron and steel implements imported from Europe and the inability of the indiginous iron producers to adopt new advances in technology".Unquote.
In real terms this would not have started to take effect much before 1550 during Portuguese partial control, though, once the Dutch, driven by the VOC, which fed on trade (and indicated by VOC stamped kastane blades for example) and the EIC of the English (though they did not apparently stamp blades of Kastane) until the modern era it seems iron/steel production would have been, at best, only scant. The break then in indiginous iron/steel production probably occured in the mid to late 1500s though some local iron/steel may have been produced in the Kandian Kingdom thereafter but dwindled further under English rule as they seized the entire country.
In conclusion I place this as possible evidence to explain our misunderstanding and the gap in proceedings possibly tricking the reader into thinking the Kastane was introduced when in effect it has been a purebred Sri Lankan Icon from its early pre European period. 
Regards,
Ibrahiim al Balooshi.