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.