One of our older TBC files is an update from a project started in trimmap, migrated to TGO, then TBC.
Updating to newer programs over the years has created a bit of confusion for the projection parameters.
This project was based off DOT control points with modified SP numbers scaled up from 0,0.
If you look at the TBC file and check the projection parameters it no longer says state plane zone x like it originally did, but all the numbers are state plane for zone x. The central meridian, scale factor, type of projection, ect.
However, through all the upgrades the scale point for the local scale modification has shifted slightly, it says N0.1', E0.05' for some reason. One of the other LS's was looking at it and figured it should be changed. I told him that you can, but it won't make a bit of difference. Where the scale point is will only shift the numbers for the coordinates by the difference between the new coordinates for the scale point and the record coordinates for the scale point times the scale factor.
So a scale factor of 1.0003 will introduce an error of 1.0003 x 0.1=0.10003 then .10003-.1=.00003' of error. Increasing the northing for the scale point to 100 and that will cause a shift of 0.03'. It doesn't matter if the coordinates are 1000' from the scale point or 1,000,000'. The same shift will apply. Of course, seeing the scale point being "off" makes the user feel the resulting coordinates should shift .1', .05', but in reality it's not an issue. The urge to "correct" it is pretty strong.