Can confirm this about 320 GA mode?
In the various FCOMs, there used to be a contradiction, or so it seemed to me.
CLB mode cannot be engaged in the FMGS GO AROUND flight phase (FCOM 1.22.30 p21). In p57, the "typical FMA at GA" shows CLB armed. I understoodd that at accel alt it is OP CLB what engages, even with NAV . Therefore, in final approach we have to select in the FCU the first at (or at or below) constraint in the missed approach procedure, if any.
In the FCOM 4.05.80 p2, I see now that this is what happens, but some time ago it was different. My imagination or it was ammended?
And in brand new models, apparently, NAV will engage, like in a take off, instead of GA TRK, unless you have preset a HDG.