"Several", but not all (I've "heard").
You got any activations that actually came off? With dates and Q counts?
I like to keep track of this stuff and finding anything other than "mega" expeditions is like pulling teeth sometimes.
As for the individual operators you mentioned:
ZS8M's QRZ page includes this discouraging note:
NOTE: All QSL cards that arrive within and before the end of 2017 will still be processed. No more cards will be available after Dec 2017.
However, the QRZ.com details says it is an LOTW member, so older Qs might still be matched (or should have been already). However, the last upload to LOTW was in 2013. Can't be sure, but it is likely that QSOs stopped by 2013 unless the DX just decided to stop uploading.
ZS8Z apparently ceased operations in 2017. Is a member of LOTW and eQSL according to QRZ.com. Cards can still be obtained, apparently.
Anyone know how many Qs they turned out? I'm pretty active and have a pretty good spot filter. I don't recall even seeing these guys spotted -- certainly didn't work them. I do have ZS8 all time, which may help explain that. Still, I should have been looking.
So, however many QSOs they made, this looks to me like another Macquarie Island case. Great if we have a resident op or two, shut out if we don't. Difficult to assess these kind of cases. Right now, though, both are on the "good" side as both have had activations withing 5 or 6 years back. Compared to some of these entities, that's damn good.