Hey cascaderailroad
Yeah, you could just be right of course, but  my main line actually equates to some 12 miles of real track that takes most consists some 10+ minutes in real time to traverse back to the "through" station.  I  certainly do not have that density of trackmarks you suggest to let the  consists going around the long twisting and convoluted main line, but  there is basically nowhere else for them to go, it is a long, looping,  reversing, tortuous mainline, but they have no options but to go around  it.
When it comes to the through station, there are loads of  trackmarks to try to stop them taking a really dumb SHORTER route, which  I know the AI does automatically.
My problem is trains going  through to platforms that are already in use, despite all of the  platforms having ENTRY and EXIT trackmarks that the session rules tell  the consists to go through.  However, they seem to have a mind of their  own, and pass the station entrance STOP/GO signals with impunity, even  though the next scheduled trackmark is not accessible.
Therefore it seems like maybe it is TS12 signalling issue rather than an AI issue ??
Any  input you guys out there with way more experience than my piffling 4+  years playing with TS will be very well received to sort out  these conundrums, but I have been writing complex raw "C language  software for business for many years, and can understand absolutely how  these problems can come about !.  It would be good however to see them  fixed in this scenario?
I bet I am doing something real dumb, but .......
Ian