Hi Jock! I cured olives from my own trees last year for the first time and here's what I found out.
Most backyard olive trees in California are Mission Olives. They are best picked green or mottled and cured then. They will tend to get squishy if picked and cured riper, but they are not spoiled. Just a few of mine in each jar (I put them in jars when I switched to the weaker brine) got squishy and I threw them out because I didn't like the texture. The other olives were fine and we are still alive! We will be picking earlier this year!
Without a lye cure they will remain slightly bitter. When you eat them, drain and rinse them (I soak mine in fresh water for a couple of hours to reduce the saltiness). Then marinate them in a little oil with: vinegar, garlic, herbs, spices, you name it. Let them marinate overnight if you can. They are lovely with a little orange peel. Any bitterness that remains becomes part of a complex flavor.
Have fun! Love ~ Debbie