Some puzzles have more than 1 valid solution, and they will all solve the puzzle.

If (for 'yellow herrings') the puzzle didn't complete even though you used all the numbers, it may be because there were empty tiles left? Accepted solutions use all empty tiles.

But, your point about not all valid chains getting a tick / locking down is a legitimate shortcoming. Right now the puzzles have a "canonical" solve used for ticked/locked chains, and hints. We rolled out a fix for the chains, but then the hints didn't make sense for some users, so we rolled it back this morning. We'll get that fixed with something more thought-through shortly.

Thanks for playing!