Also, if you're not certain, and wish to be 100% absolutely sure, do a water test before you fill it. Simple as that. And also especially pay very close attention to the sealed/caulked corners! I had a 15L once, and near the top, which was in a typical, non-visible spot, where the black trim is on the right side, actually had less than 1/4 mm UNSEALED crack in the glass/breach in the top, that was barely being held together by the tank's black trim, and which I only discovered when I did a water change! It wasn't very wide, but it was enougn to have some significant dripping out from the right side in the tiny tiny tiny little crack, which was only about half of the thickness of a mechanical pencil lead! SUCKED! Had to re-seal it with some silicone.
If you are concerned, you can reseal it. If I were concerned I would never be able to rest comfortably always thinking the tank was going to leak, regardless of what others say. I need to say, lately I have become a bit paranoid, it's something I'm working on but I feel the need to say this before I give too much advice. Maybe I should put it in my tagline.