Coffee Appreciation

but if the time after grinding is the same the speed of the shot coming through was massively different. the first batch of coffee used the same dose/tamp pressure after opening the bag as the second bag purchased 2 weeks later.
which suggests variations in grind or bean not ground coffee ageing after grinding.

When making espresso you find you need to adjust the grind almost on an hourly basis as humidity and ambient temperature affect the behaviour of the ground coffee. Unfortunately you do not have the facility to do this if using pre-ground. What may work on the day of purchase may be way too fast the next day and too slow half a day after that, even despite rapid deterioration of the coffee.

Of course, the grind will be slightly different, the grinder will have been dismantled for cleaning in the time between purchases. It gets re-calibrated but it's not gonna be exactly the same, especially for espresso where grind changes tend to have an exponential effect.

Are you comparing shots made 2 weeks apart, or consecutive shots made with coffee 2 weeks different in age? Either way, you can expect large variations in shot times. Mooks seems to be onto a winner with his £4 hand grinder.