That’s the oddest thing, I’ve never heard of the “no boxtop” rule. My family used to puzzles all the time together too. I never knew there was another way. Hmph.
The only rules we had were:
1)Flip all the pieces rightside up.
2)Crusties first (aka Edges)
3)Watch Mom. (She liked to hide one piece so when the puzzle was almost finished she’d pull out the last piece and put it in).
I haven’t ever heard of the rule either. I think it’s perfectly fine to use the boxtop, but then again, that’s how I’ve always done it.
Several years ago I was really into jigsaw puzzles, but it eventually got very boring. So I started doing them face-down (all you have to go by is the shapes of the pieces; I even made up names for the types of shapes). Then I started mixing up the pieces from two or more puzzles with similar color schemes. then I started mixing up the pieces from puzzles with the same backing color, and doing them face-down. You wouldn’t believe how long these took.
The bottom line is this: make your own rules; and if you get bored, change them.