The same concept applies. At any point you can adjust the next difficulty by looking at the PRIOR 2016 blocks.
Most sites don't do this because they are using difficulty and future difficulty to project network hashrate and to don't want to complicate the calculations with multiple difficulties.
So they do this.
At 1 block after difficulty adjustment they use 1 block.
...
At 100 blocks after difficulty adjustment they use 100 blocks.
Instead you can do this
At 1 block after difficulty adjustment you use the last 2016 blocks.
...
At 100 block after difficulty adjustment you use the last 2016 blocks.
Most sites don't do this because they are using difficulty and future difficulty to project network hashrate and to don't want to complicate the calculations with multiple difficulties.
So they do this.
At 1 block after difficulty adjustment they use 1 block.
...
At 100 blocks after difficulty adjustment they use 100 blocks.
Instead you can do this
At 1 block after difficulty adjustment you use the last 2016 blocks.
...
At 100 block after difficulty adjustment you use the last 2016 blocks.
at that point (1 block after), wouldn't using the last 2016 blocks give a better 'projection of network hashrate' ?
Of course but the math gets more complicated because each block needs to be adjusted by the difficulty at the time of that block.
For some sites simply looking to provide a quick snapshot of "current hashpower" they opt for the simpler calculations of a flat difficulty which means lots of error right after difficulty adjustment.
