Yep, if dashupdate.xbe runs to completion its tidy-up phase includes deletion of the xboxdashdata.17cdc100 directory.
However, with an Ndure setup {: correctly implemented, ahem :} it doesn't get that far, at least for all the dashupdate.xbe's I've tested so far.
Yep, dashupdate.xbe's check the certificate version of both the xonlinedash.xbe and the xboxdash.xbe ... if either is less than its own then it runs.
Btw, what certificate date does that November OXM dashupdate.xbe have and what's its byte size?