Measure lost steps on dual Y?

[markz]

Topline: is there a macro I could write for my homey.g that would let me see the delta between the dual endstops?

Background: When I set up my dual Y gantry I left in an early test line in config.g as below.
M574 Y1 S1 P"ystop+e0stop" ; Y min active high endstop switch
M574 Y1 S1 P"ystop" ; Y min active high endstop switch

So, I thought I was using dual endstops for Y but I wasn't. The result was that my CNC homed Y but it was at best homing one side of the gantry. I got low-frequency chatter at some speeds and then it started stutter-stepping and stopped moving one side at all (with a couple of emergency stop pushes in between all this). Watching a half-ton machine try to tear the gantry apart is not great.

I commented out the line and things are working again but...

What this means to me is that somewhere I lost steps so the sides went out of synch (I've been trying to tune accel and jerk settings).

Finally: It would be really cool if there were a way to see how many steps I lost by just homing and having it tell me how many extra steps one side took to hit its endstop. (mm is as good as steps). I'd also like an easy way to see which of the dual endstops are triggered (the board is out of sight).

My hope is somewhere in the object model are things I can read out and display or save but I don't know it well.