When Ad verification is enabled Advalidation will check the tags to confirm if blocking and/or monitoring has been applied.
In the case of blocking, when applied it means that the creative does have blocking enabled, but it does not mean the creative will always be blocked.
Whether an ad will be blocked or not will depend on the site the ad is potentially being displayed on. Any sites that do not fulfil the brand safety criteria will be blocked, whereas sites that do fulfil the brand safety criteria will not be blocked.
Therefore if blocking is enabled on a tag, Advalidation highlights that the tag has the "potential" to be blocked, and not that the ad will definitively be blocked.