All tide reports I know of are based on predictions, and are based strictly on known astronomical events (sun, moon positions, etc.). Therefore, there are no old or new forecasts. There is no tidal information that I know of that is real time. No tidal software can take into account the effects of wind and/or storms, therefore, no tidal predictions can be 100% accurate. When I go to the tide information in my HB, it selects the nearest tide reporting station at that moment, then calculates the tidal information for that station using the Navionics software.
I’m not sure how far in advance the Navionics software is pre-programmed for, but I’ll bet it will still be valid long after I’ve retired my HB. I have a watch that can predict the tides until 2099...not sure I’ll be around to verify the date, though.