CoS for previous financial year for tax benefit

Hi,

I'm on Tier2 General visa and my husband who was in ICT became my dependent in 2017 May. He is still working with his company who once sponsored him ICT visa.Now while claiming tax benefits,tax consultant is asking us to get CoS from his company.Is it possible to get backdated CoS?His ICT visa would have expired by Mar 2018(ICT CoS was till Mar 2018)Tax consultant is asking my husband to get Cos for the period from Apr 2018 to Mar 2019.Will it be possible?
I cannot claim any benefit as I was not paying any household bills.
Has anyone ever experienced this situation?Any leads would be appreciated.

Thanks in advance.

Now while claiming tax benefits,tax consultant is asking us to get CoS from his company.

What tax benefits exactly?

His CoS would only be a number with his details, it is nothing to do with Taxes.

It seems since we are temporary in this country ,we can claim HRA benefits.For that they need proof of his temporary employment.Hence asking for CoS.

What are hra benefits??