First, you should always seek qualified legal counsel before taking any action or making decisions. But generally speaking, a will covers only those assets that do not have a beneficiary designation. If an asset has a beneficiary designation, it considered "under the law" rather than "under the will."
Examples of assets that are "under the law" include retirement accounts (401k, IRA, Roth IRA, etc.), life insurance, annuities, and other assets that have transfer on death (TOD) or payable on death (POD) clause. At someone's passing, these assets will have to be distributed by force of law and the contractual nature of their beneficiary designation, not the force of the will.
This is an important reason why wills should be reviewed periodically, along with all beneficiary designations. Life is rarely simple! I hope this helps.
If there is a beneficiary stipulated for a particular retirement account (IRA, 401k, ROTH), the designated beneficiary will generally be entitled to the account, irrespective of a will or trust arrangement with general inheritance language. As Jonathan states, you should always check with counsel to confirm the particulars of your facts and circumstances.
