Glad you found something that works for you.
Sour Crop can take a long time to resolve since it's an infection. The article linked previously and again below is the treatment protocols I follow. They work for me:)
Annually? You mean they produce Cecal poop only once a year?
Cecal poop is produced in the Ceca and it is seen about once out of every 8-10 poops, so you will see quite a bit of Cecal poop daily.
Yogurt alone will not clear up a Crop that has turned sour, it can be given in very small amounts...
10 weeks old?
Looks like normal cecal poop to me.
If you are checking crops during the day when they have been eating/drinking, you certainly will feel watery/filled crops.
Re-check crops first thing in the morning before the birds have had anything to eat/drink, if the crops are not empty...