On the power grid, electricity flows in the least resistive path. That is independent of purchases like California buying out of state power from a wind farm, the actual energy arriving is from the same least resistant path. Power companies have installed metering to register power into and out of these interchange substations. For a single company, like my old company Toledo Edison, we had 11 interchanges. My department tested these meters and associated equipment. So our company as a whole knew if we were into a net sell or net buy situation at any moment.
Companies mostly have this run or managed by an energy system to know if we need to buy or sell. Independent of any of that, the power flows independent of the scheduled buys or sells. It is after the fact that the net flows are determined and an economic adjustment is made. It can be complex.
So as I said before, this is all a political stunt. California has no basis other than a piece of paper who they are actually getting power from. It is all just a net in or out situation for each and every company.
No doubt some executive in California improved his resume by all these shenanigans. Maybe enough for that sought after promotion. Ya know, these are usually poor choice executives.
California has long screwed electric customers of all sorts and the California electric utilities. It is a long standing issue. Additionally California as in many states go through hell to get state approvals for a new plant. California is a net importer of energy and has been for quite awhile.
California and many other states have this fear of a power plant of any sort but especially a fear of nuclear power. Those opposing power plant construction also provide significant barriers to constructing transmission lines. Delays are probably the largest cost element in planning for their companies future needs.
Solar plants are a boondoggle. They are government subsidized which shows they are not economically viable. They are mostly sold on appearances. Spain went this road a few decades ago, and has largely closed all these wind plants.
When you next hear someone promoting wind, solar, or some other free power sounding system, tell them to put that concept where the sun doesn't shine.