Okay, thanks Philipp.
Anyone can confirm that the tool diameter entry can have at least 10 decimal place entries using JJWHarris’s .e10 file (https://forum.v1e.com/uploads/short-url/oUnhXPfCIX7Hi1hvpjcijX5t4Sx.zip). While zoomed into the top-left corner enter 1.9999789808 and the corner will be cleaned up (1.9999789809 is too big). For the rightmost-bottom corner (worst) the maximum diameter (to clean up all corners) is 1.9995021109. Note: this has no practical value and I would not change the tool diameter unless it solved an issue on the Preview screen.
Most (all?) numbers stored in the Estlcam configuration file (including user inputs, e.g. Distance per revolution) have 16 decimal places and it may be that most (all?) user inputs could have 16 decimal places as well. While the stored numbers have 16 decimal places they are somehow rounded and not exactly the number entered, e.g. 8.016 = 8.0159997940063477 (-.0000002). That same/similar rounding could be the cause of the occasional edit screen issues.
The G-code Preview screen is different because the only numbers involved are 4 decimal place (G-code default) path coordinates, i.e. The Preview screen is what matters.