I have found that as I talk with some people about their Patriarchal Blessings there has been an underlying assumption that their immediate, initial "understanding" of the blessing is correct - that if things don't happen as they assume the blessing describes, then the blessing is "wrong". Two of the best examples of this are those statements that deal with marriage (including children) and longevity.
Let me use two specific examples:
1) Someone is given blessings related to adult life, then that person dies before reaching adulthood. If the Patriarch were seeing the future, wouldn't he have stopped the pronouncement of blessings before marriage and kids and career and education and adult church service? To me, this is the easiest example to address, since I surely wouldn't want it to be stated (or even implied) in a daughter's blessing that she would die as a teenager. I think that would be cruel and would change totally the way she would live her life - and generally not in a positive way.
My takeaway from this example:
A Patriarchal Blessing is a guide focused on a full life. Whether or not each individual lives that full life is not the job of the Patriarch to ascertain - with rare exceptions that prove the rule. There generally is the "dependent on your worthiness" clause (although I know of one case where that clause does not appear and the blessings are phrased in a way that makes it clear that worthiness will never be an issue - which has been correct), but I believe there also is an underlying, unstated, assumed "dependent on the vagaries of life" clause.
2) Someone is told they will marry and raise children, but she reaches the age where she no longer can bear children and is still single. This is tougher, since it seems like such a straightforward promise.
I believe there might be an eternal element to these blessings, but I try to use that only as a last resort - since I believe these blessings are intended primarily as a guide for this life. So how do I reconcile the marriage and children promise?
This is where my own view gets a bit unorthodox. We are conditioned (properly, I believe) to interpret statements like this in accordance with the "Gospel/Church ideal". I believe that must always be our initial read, unless prompted by the Spirit. Therefore, this statement is taken to mean, "You will marry in the temple and give birth to sons and daughters . . ." Many times, however, that simply isn't what actually is said by the words on the page.
Non-temple marriage and adoption are legitimate fulfillment of the actual statement, but it is easy to ignore those options in life if reading only in light of the "ideal". If a person reaches 30 (arbitrary number pulled out of thin air) and has no immediate prospect for a temple marriage, I have no problem whatsoever with that person looking actively for a non-temple marriage - if that person feels inspired to do so. I know that is heretical to many, and I don't preach it as the general rule, but I do know that exceptions do exist for every rule, and 50,000 out of 5,000,000 still would be only 1% - a true exception.
I haven't even gotten to the fact of others' agency and how their choices impact our lives. I think that plays into a lot of the statements in our blessings and whether or not they come to full fruition.