When you copy paste the play log and start the calculation, the server is contacted to get the current game ELO points.
With the latest ELO changes the game ELOs are updated instantly so the server now returns the already updated ELO points for the games which may cause some slight differences in the results.

I have made some changes to restore the previous ELO points for a game (i.e. before the update took place) approximately with the assumption that the game was not played in the meantime. Still the results may NOT be so exact as expected.

How close is it?

So out of curiosity, I played 10 games to compare the results with my calculator.

So I copied those 10 games:

And pasted into the input box as below and here is the result: