How to agree 2 sets of data on multiple sheets


Insurance company that processes claims from clients. Once a contract is entered, the client is assigned a unique reference number and the date of contract entry is recorded.

If I have two excel sheets with data;

1. Sheet 1 has claims made by clients showing:
- Dates of the claims
- Unique client reference number.

2. Sheet two is a record of existing clients showing:
-Unique reference numbers
-Dates on which contracts were entered

The claim date may not be before the contract entry date.

How do I check that:
1. That the reference numbers for both sheets agree and that the date of the claim per Sheet 1 is after the date of contract entry per sheet 2? So basically, how to check that the claim dates are bigger than contract-entry dates for each unique customer reference number?
2. Can this be integrated into one sigle function?

Thank you for your assistance. This will save my life.