The Rouge There is no need to extrapolate form. The market moved until the last day of the season. Let's say Newcastle win their first 6 games - they would be on 18 points with 32 games remaining (and presumably playing better than expected). So the bookies may change their price to sell 71-buy 72.5. these recalculations of current prices are done after every game - so we can produce as it stands league tables every 5 games or so.
I'm buying at the start of season places and interested in the result at the end. I don't care what the bookies think midway through the season. I care what the clubs form suggest the end of the season will be like. The bookies will be basing stuff on that anyway.