Text icon comes and goes on Voice Mail messages

Why is the text icon available on some voicemails and not others? And why is not always in the same spot?

Sometimes it's between the phone and the trash icon.

Sometimes you have to click the 3 dots to see it.

Sometimes it's not there at all.

I thought maybe somehow ring central knows if it's a textable number and takes it away if it is not, but that's not the case.