In the section where we speak about which trees suit the halacha requirements, you mention
"Chemdat Avraham 2:10 says it is not lechatchila but if there is no other tree you can make the Bracha"
How would I know if the fruit tree I am making my Bracha on is going to carry fruit this year or not? It is a chance one has to take, isn't the question rather about after the fact, meaning I have made a Bracha on a fruit tree that I have now seen didn't carry fruit this year, was my Bracha valid or not?
A: I believe that if there's an established pattern that a certain tree grows fruit, there's no concern that it won't bear fruit this year and you may make the bracha (see, however, Mishna Brurah 8:20). The case in which your doubt is relevant is a young tree which never grew fruit but may grow fruit for the first time this year. In such a case, then you're right the argument of the Chemdat Avraham is only relevant after the fact.
Rabbi Yisrael Meir Kagan (1838 – 1933), known popularly as The Chofetz Chaim from his book on the laws of Lashon Hara, was an influential Lithuanian Rabbi, author of the Mishna Brurah as well as the Beur Halacha which is in more detail and the Shaar Hatziyun which quotes sources