Plates were required always... But plates are sent by mail (mostly), after some processing, so there's a delay between first registration and when the plate can be installed. California finally started doing temporary plates in 2019.
California has some mile posts and some numbered exits, but you're expected to report location by named exit. Ex: North on the 405, right after Pico Boulevard. Etc.
The California highway system was extensive before federal highway standards were developed, and California was exempted from exit number requirements. In ~2000, California decided to add exit numbers 'over the next ten years' as signs are replaced; twenty years later, it's still not complete, but Google still likes to give directions with exit numbers only, as if that were useful.
California has some mile posts and some numbered exits, but you're expected to report location by named exit. Ex: North on the 405, right after Pico Boulevard. Etc.
The California highway system was extensive before federal highway standards were developed, and California was exempted from exit number requirements. In ~2000, California decided to add exit numbers 'over the next ten years' as signs are replaced; twenty years later, it's still not complete, but Google still likes to give directions with exit numbers only, as if that were useful.