Pardon me, I don't think that's it.
I think it has to do with the difference between RoC and TFT. Don't quote me on that, but, I have noticed the old RoC maps have it and the new TFT ones don't.
Those that were originally coded for RoC and then modified into TFT vs. TFT orignals which don't seem to have it at all.
But it could be something else.