I don't have Web access on my computer currently so maybe I'll be able to send it tomorrow.
I did some more testing with it. I recorded for 27 seconds and observed the final location. It varied maybe a thousandth of a pixel so it's not exact, and I can see how it can get further off as the recording gets longer. Dt does indeed vary slightly because the time between frames varies a little, and the the minimum frame rate is only used if dt is greater than it.
So instead I tried a framerate limit slightly higher than 60 like 64.
On chrome it worked well in giving me a constant dt and after a 37 second recording the end position was exact every time.
Edge didn't work so well with that. I was still getting a different dt occationally which made the end position off by around a pixel after 37 seconds. I tried 9999 but looking at dt it seems 1/120 is the minimum dt on my machine for chrome and edge.
But that also made my game run at half speed. Does your game run at the same speed?