Contractor notifies of a prevention event due to Covid

My first question here, so please forgive me if this has been covered previously.

I am working on a programme where the main contractor has notified of a prevention event under clause 13.1 of NEC 3 as a key material supplier (sub-contractor) has notified them of a disruption to production due to staffing issues caused by Coronavirus. The contractor has advised that a key date which we need to shutdown the network for testing and commissioning will be missed. The deliveries from this supplier has been very unpredictable for the best part of 6 months.

Firstly we suspect the material supplier has staffing issues due to its own internal cost reduction measures, it is taking as part of a well publicized on-going restructuring programme which included a shut down of one of its factories last year and transfer of production to the site in question. Hence the premise that this event could not be foreseen or avoidably mitigated by the Contractor or its Subcontractor is somewhat hard to accept. Last year they tried to reschedule all the deliveries but back-pedalled after significant commercial pressure and stakeholder management.

Secondly as a result of missing the key date in question, by only a 6 weeks, we would lose our planned shutdown of the network to do the testing and commissioning and the Employer may be unable to provide an alternative shutdown period for another 7 months as the Network is a critical national asset and can only be upgraded via planned outages negotiated months in advance. In this case, if Contractor cannot mitigate the delay and the key date is missed, will it be a valid “prevention event” leading to a valid compensation event CE?
If this results in a CE, will the Contractor be entitled to the 7 months EOT minus the 6 weeks that they missed the key date (i.e. 6 weeks was the Contractors delay and the rest due to inability of the employer to provide a different test slot) ?

All parties are currently exploring risk mitigation options but I would like to know how such outcomes above will be covered by NEC should the key dates be missed and the programme delayed.

Thanks in advance. Appreciate your insight into this issue.

Any replies to this would be appreciated.
Many thanks.