As someone born in the US, who has listened to and watched _many_ UK books and productions, and now lives in Canada, the various differences in pronunciations still often catch me out. 'an-SILL-a-ree' wouldn't bother me, even though I'd grown up with 'AN-sill-air-ee', but others still grate. OTOH, I now find the US pronunciation of 'praah-ject' instead of 'pro-ject' positively annoying. Even when I do it myself.
As for rot-see -- my teachers always referred to ROTC, but no one who was in it ever used anything but rot-see. I have no idea what's current, however.