VHDL define range as previously defined range + offset
I want to make this one perfectly clear, so I'll keep it short. VHDL describes hardware, so what you are asking for is a piece of hardware to run off previous values. These stored values of which you speak are memory. So to do what you want I would suggest a latch, where based on a condition, you latch a value somewhere to act as a stored value, and then work off the output from the latched memory.