Your Will only covers your desires that you have put into it. If you leave something out of your Will then it can be challenged.
For example if you have a family heirloom that you want to leave to a specific child and you don’t record that in your Will then other family members can contest it.
It’s important to be specific about the details of what you want left to specific individuals or organizations. So no, your will is not invalid but it may not be complete at the time of your death.