I'm not sure if you're aware, but the network was a wee bit disrupted yesterday. The fact they've found units to run these services at all is pretty good going, given how may ended up in the wrong place, and that at least 3 suffered storm damage.
Also, RTT isn't all that accurate when it comes to TFW allocations, and this 170 example is a case in point. There is no chance you'll ever see a 170 on this service, and indeed it's actually a 158.
It might, but it's not that easy to swap the 150 and 175 around if the former is starting it's day in Crewe and the latter in Cardiff.