Can not sending a LOCI to a SCEA school where one was deferred work against you? The high school did send a letter to SCEA college about being chosen for the Cum Laude Society, however, it occurs to me that does not express one’s continued interest. Although there are updates, there is nothing extraordinary. Or should a LOCI be sent now ( tomorrow is March 1st, may be too late for that)? My thinking was that applying SCEA shows strong enough interest and a LOCI was not needed. Thoughts?
I would send one
I think it is fine either way. The schools that have SCEA generally assume students deferred EA are still very interested in attending.
I’m thinking they are more likely to admit those who take the time to express continued interest. They don’t know if u perhaps ED2’d somewhere else after getting the deferral. Many who are deferred simply move on. They won’t know your intentions unless u express them. Send the LOCI.
I agree with @happy1 . The fact that you indicated SCEA means that you are referring to HYP, all of which have the attitude “well of course we are your first choice.” 
So, it won’t hurt to send (probably won’t help either), but if you do send, you will know that you have done everything possible. Good luck.
If it was a wait list, I would say “definitely!” Colleges want to admit students who would attend.
But with regular decision, you haven’t even gotten a decision…I agree, why send a LOCI at this point?
You applied SCEA…you want to attend that school in particular.
It won’t hurt. If brief at this busy time.
And it will take away any potential regrets.