Your client should have their 1444, their bank statements, etc. Also, you or your client can see what is available for their Stimulus info at these links:
I hope they'll have a look up tool as most ppl probably did not keep the 1444 Notice. I foresee lots of delayed returns this year.
@TaxGuyBill noticed the other day the draft F.1040 instructions (which I also verified) indicate that taxpayers can use the webpage in @qbteachmt's first link above to check the amounts of EIP paid to them if they can't locate their Notice 1444.
---------------------------------------------------------------------------------Still an AllStar