In an FT8 contest on 70cm recently there was a special event station in France that worked several of us in the contest, but they didn't send their grid location. I looked them up on QRZ and manually entered it into my log.
When the results came out the adjudicator said that they had been unable to confirm the grid locator for that station, so all of us that worked them were docked those points from our totals.

So, no, you can't 'just look it up'...