Yeah, that's been an ongoing problem. TNE kind of had a minimal reason for changes, though tracking G-hours gets to be too much spreadsheets in space.Sorry, had to laugh, since DSMS seem to be retconned to account for the 1000D retcon.
That's okay, TNE got rid of m-drive entirely, and that's the one thing I actually liked about it... G-hours. Drastically altered in-system travel assumptions and made micro-jumps more practical.
It's kind of like how the Honor Harrington universe has Traveller-like drives, and it's all great in text. But when they tried to game it out in 3D it just went to crap due to the complexity. Gaming means simplification and I'm all for that. I just prefer that the simplification remain consistent. And consistency across the decades/publishers has been a tad lacking here.