A lot of biblical prophecies are failed prophecies because they are so vague that there are multiple interpretations of when they were fuflilled.
RationalWiki has a vey good article on biblical prophecies:
There are numerous Biblical prophecies, some vaguely fulfilled, others strangely unfulfilled. Of course, like the Bible, the Quran also contains what its followers maintain are fulfilled prophesies. Christians tend to find these unconvincing or silly — which is coincidentally the attitude which...
rationalwiki.org
They have some very good standards on what terms must be met for a "true biblical prophecy":
Criteria for a true prophecy[edit]
For a statement to be Biblical foreknowledge, it must fit all of the five following criteria:
- It must be accurate. A statement cannot be Biblical foreknowledge if it is not accurate, because knowledge (and thus foreknowledge) excludes inaccurate statements. TLDR: It's true.
- It must be in the Bible. A statement cannot be Biblical foreknowledge if it is not in the Bible, because Biblical by definition foreknowledge can only come from the Bible itself, rather than modern reinterpretations of the text. TLDR: It's in plain words in the Bible.
- It must be precise and unambiguous. A statement cannot be Biblical foreknowledge if meaningless philosophical musings or multiple possible ideas could fulfill the foreknowledge, because ambiguity prevents one from knowing whether the foreknowledge was intentional rather than accidental. TLDR: Vague "predictions" don't count.
- It must be improbable. A statement cannot be Biblical foreknowledge if it reasonably could be the result of a pure guess, because foreknowledge requires a person to actually know something true, while a correct guess doesn't mean that the guesser knows anything. This also excludes contemporary beliefs that happened be true but were believed to be true without solid evidence. TLDR: Lucky guesses don't count.
- It must have been unknown. A statement cannot be Biblical foreknowledge if it reasonably could be the result of an educated guess based off contemporary knowledge, because foreknowledge requires a person to know a statement when it would have been impossible, outside of supernatural power, for that person to know it. TLDR: Ideas of the time don't count.