Actually I have no data to back up the ‘most’. What Vero can and can’t do was discussed at length in HDR too dark on TV. Somewhere in there it says some seis are being read and some aren’t and it’s clear what was done with the default mastering data at that time.
We looked at trying to extract the sei data by other means as a workaround but it wasn’t practical. It would be even less practical for HDR10+.