I've seen it listed both ways as well.
My take is that it was once recommended to deworm with a less complete dewormer, such as wazine, that kills less species of worms before deworming with Valbazen To get rid of some of the worm load so the Valbazen wouldn't kill everything all at once and cause the chicken to die from trying to pass a heavy worm load all at once.
However, now it seems that the Valbazen is recommended for first deworming because it is a slow kill, unlike the wazine which kills faster and could still cause heavy worm expulsion loads. This also prevents two consecutive egg withdrawal periods.
I'm about to deworm my pullets and cockerals with it for the first time next week. I added some older pullets to my flock and have noticed tapeworm segments in their poop
I regularly mix DE into their feed, so I'm thinking I'm seeing them because the DE is damaging the worms. Still, it's disgusting and I want them dead so I want something stronger. This week I am "prepping" them with rooster booster multi wormer, but next week I will deworm with the Valbazen. I'll let you know how it goes.