Annualized returns are not fixed and will generally decrease over the next 8 years. The total voting reward token allocation will decrease over time. Also, as more ICP is staked, the fraction of the “total voting reward token allocation” received by each individual will decrease. You can increase your dissolve delay any time which will result in greater rewards. Also, if you have not started the unlocking of your neuron, then your neuron age is increasing, which also results in increasing rewards. All of these factors impact annualized returns and make it difficult to predict what the actual rewards will be in the future. An excellent calculator that can be used to test various scenarios can be found here: ICP Neuron Calculator.