Good idea. Here it is
SELECT DISTINCTROW tblTestsWithInvoices.ArbitraryIncrement, tblTestsWithInvoices.InvoiceNumber, tblTestsWithInvoices.TestID, tblTestsWithInvoices.seqInvoiceNumber, CheckIn.Contact, CheckIn.SampleRepresents1, CheckIn.CIQNumber
FROM CheckIn RIGHT JOIN tblTestsWithInvoices ON...