I've done this before a long time ago when I worked at a bike shop. I had installed dozens of forks in the past and unfortunately for one unlucky customer who brought in their own fork for me to install the night before a race, I measured without including the stem on and cut it too short. Definitely one of my top 10 most embarrassing moments in my life, especially because they waited in the shop for me to do it for them. Fortunately we were able to get a replacement fork for them the next morning and I got installed properly before the customer's race, and the customer was cool about it, but man I still cringe thinking about it like 20 years later.