Notice that when referring to the great tribulation, all of the following translations except two, speak of it as THE, which designates ONE GREAT TIME OF TRIBULATION.

I told him, "My lord, you know." He said to me, "These are those who came out of the great tribulation. They washed their robes, and made them white in the Lamb's blood.  (WEB)

And I say unto him, My lord, thou knowest. And he said to me, These are they that come of the great tribulation, and they washed their robes, and made them white in the blood of the Lamb.  (ASV)

And I said to him, My lord, you have knowledge. And he said to me, These are they who came through the great testing, and their robes have been washed and made white in the blood of the Lamb.  (BBE)

And I said to him, My lord, thou knowest. And he said to me, These are they who come out of the great tribulation, and have washed their robes, and have made them white in the blood of the Lamb.  (DBY)

And I said unto him, Sir, thou knowest. And he said to me, These are they which came out of great tribulation, and have washed their robes, and made them white in the blood of the Lamb.  (KJV)

And I said to him, Sir, thou knowest. And he said to me, These are they who came out of great tribulation, and have washed their robes, and made them white in the blood of the Lamb.  (WBS)

"My lord, you know," I replied. "They are those," he said, "who have just passed through the great distress, and have washed their robes and made them white in the blood of the Lamb.  (WEY)

and I have said to him, 'Sir, thou hast known;' and he said to me, 'These are those who are coming out of the great tribulation, and they did wash their robes, and they made their robes white in the blood of the Lamb;  (YLT)