That's how every alphabetic jigsaw puzzle I've ever attempted works, so I assumed it was the case here. Although now I see that the special instructions aren't worded the same, so there is a possible alternative interpretation.
I found that one an absolute stinker, mainly because I couldn't parse half the clues, and in this format of puzzle you need to be 100% certain of most of the answers before you can start filling in the grid.
Sometimes I really like Paul. But not today.