Applying a glass screen protector to an already broken screen will not resolve existing damage, or prevent additional cracks from appearing. If you intended to pursue a warranty claim, you should have done so at the earliest opportunity - and not waited a year or more before bringing a potential claim to the manufacturer.
It is notoriously difficult to prove that a crack is the result of a manufacturing or material defect. As such, screen damage is often excluded from warranty claims.
If you had the foresight of opting to purchase Apple’s AppleCare+ plan, if still active, you will have the security of being able to make claim with Apple regardless of fault. In such circumstances, a small excess/deductible charge is made - and you will receive a replacement (usually a reconditioned iPad of the same model and specification) iPad.