I have a few thoughts.

For plaster, try a magnetic stud finder instead of an electronic one. With any luck (and luck you will need) your lath is wooden and the magnet will stock on the nails. You need a high powered neodymium magnet, not just a fridge magnet for this. If your magnet sticks everywhere, your lath is made of ferrous metal, and you'll have to use a drill. Stick with a small bit, of course.

Joists aren't 16 to 24 inches apart. They're 16 or 24 inches apart, on center. That was the case even 100 years ago. In some cases, 19.2" is the standard joist spacing. Check those three distances from your first hole.

Your joists could be running the opposite direction of what you'd expect. They normally span the narrowest dimension of the house, but some run the longest length of the house. Try those three distances over the other axis, too.

At that age, there is a good chance that your ceiling joists are nailed to studs. If you can find the studs on opposing walls, the joists should run end to end on the outside of the studs.

Good luck!