Survivorship is a choice, not an assumption
Under C.R.S. § 15-15-203, a multiple-party account can be set up either with or without a right of survivorship between the parties. Having more than one name on an account doesn't automatically mean the survivor gets everything — the account's own terms determine which way it works, and that's true whether the account was opened before, on, or after July 1, 1990.
How the surviving share is calculated
For an account that does carry survivorship, § 15-15-212 treats a surviving spouse differently from other survivors. If a surviving spouse is among the account's parties, they receive the amount the decedent was beneficially entitled to immediately before death. If none of the survivors is the decedent's spouse, that same amount is instead split equally among however many parties survive, on top of what each already held — and the right of survivorship continues among whoever is left.
P.O.D. designations layer on top
An account can carry a P.O.D. designation alongside its party structure. While any party to the account is still alive, the ordinary survivorship rule applies first. Only once the sole party, or the last surviving party, has died do the funds pass to the named P.O.D. beneficiary or beneficiaries — in whatever proportions the designation specifies, or in equal shares if it doesn't specify different amounts. If a named P.O.D. beneficiary doesn't survive the last party, the remaining beneficiaries take proportionately more; if none survive, the funds fall into the estate of the last surviving party.
How a bank verifies who gets paid
A financial institution can pay one or more of the account's parties on request, regardless of whether another party is disabled, incapacitated, or already deceased. To pay a deceased party's personal representative or heirs instead, the bank needs proof that the deceased was the last survivor of everyone named on the account — and even then, only if the account isn't one that carries a right of survivorship in the first place.
Life insurance and retirement accounts
Life insurance and retirement accounts like a 401(k) or IRA follow the ordinary rule: the named beneficiary receives the asset directly, outside probate, as long as they're alive when the owner dies. Either one becomes part of the probate estate only if no beneficiary was ever named, every named beneficiary predeceased the owner with no contingent beneficiary in place, or the policy or plan names the owner's own estate.