Minister for Children Katherine Zappone has said Marion Reynolds, the independent reviewer overseeing the targeted sampling of approximately 150,000 adoption records to uncover incorrect birth registrations, will report to the minister by the first week in October.
Ms Zappone's department has also explained that the figure of 150,000 comprises an estimated 70,000 records from former adoption societies which are now held by Tusla; 30,000 relevant records held by the regulator, the Adoption Authority of Ireland; and a further 50,000 or so records held by a wide range of existing and former adoption agencies.
The terms of reference for the inquiry, published this afternoon, says Ms Reynolds' report will be delivered within four months of a sampling methodology being established.
The minister's spokesman told RTÉ News that agreement on the methodology is expected in two weeks' time.
They said that Ms Reynolds' report will recommend to the minister "what further form of investigation or analysis, if any, would be appropriate, having regard to the extent of usable information emerging from the initial sampling process".
The parties tasked with devising the methodology are the reviewer, Marion Reynolds, Tusla - the Child and Family Agency - and the Adoption Authority of Ireland.
Ms Reynolds is a former Deputy Director of Social Services in Northern Ireland.
The statement accompanying the terms of reference recalls that the Analysis of Adoption Records relating to Incorrect Registrations has been prompted by the minister's revelation on Tuesday that Tusla had identified documentary evidence of 126 incorrect registrations of births in the records of St Patrick's Guild, a former Catholic adoption agency, covering the years 1946-1969.
It says a marker placed on some files specifying that the child concerned had been "adopted from birth" had provided the Tusla investigators with their vital clue.
The statement underlines that the practice of incorrect registrations had been extremely difficult to prove in most instances "because of the deliberate failure of those involved to record any information about it".
But, it explains, the label on St Patrick's Guild's records made it possible to identify possible cases and to pursue them further.
"There is therefore an opportunity to pursue a definite line of enquiry that has not presented itself up to now," the statement adds.
"Clearly it would be a huge task to carry out a detailed examination of some 150,000 records dating back to the 1900s, so a targeted sampling exercise of the records in the possession of Tusla and AAI is prudent in the first instance at least.." the statement explains.
A spokesperson for Minister Zappone has said she plans to publish Ms Reynolds' report.
Dept of Foreign Affairs comments on adoption files held by National Archives
The Department of Foreign Affairs and Trade has said that about one third of the requests it receives for information on children sent abroad for adoption are not linked to the 1,000-plus files on the provision of passports for prospective adoptees.
In a statement the department says the files originate from the late 1940s to the early 1970s.
But it emphasises that they are not a comprehensive record of all children sent abroad for adoption.
The department was responding to queries from RTÉ News about the 1,118 files which the National Archives have said they store for the department.
An archive's spokesperson said most related to individual applications but a small number involved more than one child.
They relate to the period 1942-1967 and are closed to the general public.
The archives say requests for access to any information contained in them should be made to the consular section at the Department of Foreign Affairs.
The department's statement also confirms that it is assisting the Commission of Investigation into Mother and Baby Homes which has access to its files.
Comparing the statements, it appears the department holds hundreds more files than the tranche referred to by the National Archives.
The department added that the draft Adoption (Information and Tracing) Bill 2016 requires it to transfer responsibility for its adoption files "to the custody of the Adoption Authority", a proposal it says it welcomes.
Tusla is operating a Lo-CALL number 1890 805 665 between 10am and 4pm on weekdays for anyone who may be seeking information and additional information is available on the Tusla website.