When I go to attach a territory it informs me of a potential stability loss but it doesn't show me how much.  It should.  I have to look it up after so Quick Save / Load but that's absurd.  Does it change is it always -20?

It's always a flat -20. It gets more complicated if the territory already contains districts that have a stability penalty, i.e. you stole the outpost from an enemy who had it attached to a city and built there, or you built a district on the outpost with influence like a Harbor, or there are any other modifiers.to stability from tenets, LTs, special districts, etc... so yeah, a tooltip would be nice.

This is still an actual issue. It can vary wildly depending on (based on what I've seen so far) difficulty setting, age progression, owned or stolen, many other things. It's not at all clear what impact this action would have, and I've had 100% stability to 0% stability just from attaching 1. So, big issue here.

I also had a similar problem, It can vary greatly based on the difficulty level, age development, if the player is possessed or taken, and a variety of other factors. cookie clicker

A tooltip about this would be nice.

Beyond a tooltip, a "Merge Cities" dialogue would be phenomenal to let you know what your new FIDSI numbers and stability would be, as well as just how bad the new city would be starving as the exponential population requirements overpower the linear food gain.

Agreed with the main argument - Stability loss needs to be in the tool tip.

I don't know how you attach territories, but I do so by selecting a city an then clicking attach next to one of its adjacent outposts.

In this way, I'm not even told that there IS any stability penalty.

So, yes, please include a -20 or whatever the number is below the Attach button.

And I also agree with RedSirus,

Sometimes it is not worth attaching an outpost if it sends your city into starvation.

So, yes, a preview window that would show the resulting city stats would be nice.

Without one I either save\load or attach\detach and morn the influence loss.