More than 430 smear test samples were allowed to expire before being tested, the Health Service Executive has said.
It said that the women affected were written to on 4 July and invited to attend for a repeat smear test.
The HSE said the figure of 434 samples expired, covers the period up to the start of 1 July.
The slides expired for a number of reasons, in particular, samples not being transferred to slides in time in laboratories because of recent changes in laboratory provider services due to the backlog.
The expiration of slides happened particularly during periods of significant testing activity and also with changes in the laboratory provider from MedLab to Quest and the Coombe Hospital.
The HSE said that other reasons for slides expiring can be a delay in GPs sending samples to laboratories and vials being damaged in transit.
Because of the backlog of tests, Medlab Pathology in Ireland said in May that it would not take on new tests, in order to clear its backlog first.
It is understood that new samples continued to be sent to MedLab and had to be transferred to the HSE and on to Quest or the Coombe Hospital for testing.
Some of these expired as a result.
Under the CervicalCheck programme, a sample must be sent to a laboratory and transferred to a slide within six weeks of being taken.
After six weeks, the sample is deemed to have expired and cannot be processed.
The HSE said that where this occurs, CervicalCheck has a thorough process to communicate with women and GPs.
A woman is advised by letter from CervicalCheck that her sample could not be processed and is recommended to have a repeat test at least three months after her previous test.
This is to allow sufficient time for the cervical cells to grow back and another test to be taken.
A woman's GP is also notified of the need for a repeat test.
The HSE said that expired slides are generally low in number and it monitors these rates to ensure they are within its quality assurance standards.
It said that the expiry rate for CervicalCheck from April to October last year was .29%, an increase on the 2017 rate.
This smear test expiry issue is not related to the non-issuing of results to more than 800 women from a Quest Diagnostics laboratory in the US, due to an IT problem, covering the period from last October to 25 June this year.
That matter is the subject of an independent review by Professor Brian MacCraith and his report is due to be completed and submitted to the HSE chief executive on 2 August.
This expired sample problem is also not related to the 11,500 HPV tests performed on out-of-date kits at Quest between 2015-2018.
Meanwhile, 'Sharon', the woman whose case helped uncover the IT problem, has told RTÉ News that she still has not received a full report on what happened in her case, despite it becoming public 14 days ago.
She has met Prof MacCraith for his rapid review. She has also been in communication with Department of Health and HSE officials seeking full information on what occurred in her case.