Just installed SW2018 SP0.1 and started exploring by looking at some of the Samples > whatsnew parts.
I open tab_and_slot.sldprt (file date 10/12/17) and saw that warning triangle on the save icon (Older Version File). (same for the other sample files).
When I looked at Property Summary, I see it was last saved with SW2018 PR1.
I guess that reinforces the advice that PR1 is to be considered as just a "final beta". Thus we should uninstall all Beta and PR releases before installing the first production release (SP0) which is actually SP0.1 for 2018.