Have you ever heard of the lost 10 tribes? When the Kingdom of Israel fell to the Assyrians, the 10 tribes that inhabited the kingdom were dispersed and lost from the Jewish world. They were exiled and they never came back. There was some hope that they'd come back after the ending of the Babylonian exile of the Kingdom of Judah, but they still did not come back. Centuries later, Rabbi Akiva made a statement on the status of the lost 10 tribes of Israel:
"The ten tribes will not return, as the verse says (Deuteronomy 29:27), 'And the L‑rd uprooted them from upon their land, with fury, anger and great wrath, and He cast them to another land, as it is this day.' Just as a day passes and it will never return, so too, they will be exiled never to return."
Further more, Rav Shimon ben Yehudah says:
"If their deeds are as this day’s, they will not return; otherwise they shall."
Essentially it depends on whether or not they repent according to him. Now why do I mention this? Because it plays a key roll into your question. Let's consider the descendants of "many Hispanics who moved from Spain and having their family line coming from Jewish blood" as a lost people. Let's put them on the status of a lost tribe because they have not been involved in the Jewish community for years and have assimilated into their surrounding culture. Even if you can show DNA tests proving that they have Hebrew blood, it does not make them Jewish. There needs to be a clear distinction between being Hebrew and being Jewish. As R' Yochanan in the Talmud puts it, when Esther refers to Mordechai as a Yehudi, it means he actually fought against idol worship. He wasn't Yehudi because his father or mother was a Hebrew, but because he stood up for his beliefs, and that's commonly how we use the word today to describe a Jew or Jewishness.
So to conclude, it doesn't matter. Blood does not play a significant, major role on whether or not you're Jewish, especially if the last practicing Jew in your ancestry was many generations ago. They aren't Jews who don't know it, contrary to what many might say.