Okay, so here's the thing. There's two primary internal (as in what your brain stores) knowledge bases you will face with candidates.

Intrinsic knowledge is something you know without needing to lookup. It can be relatively quick to access (as its cached memory. Note that I say cached as this becomes important later in my rant) and its "offline" which means the candidate can recall this information in a pinch. This type of information is important in crisis like scenarios but the real value in this kind of information is not actually in being able to recall it off hand but that it aids significantly in the "other" type of internal knowledge base described below.

Referential knowledge is what most people (IT especially) would consider their Google-Fu. They may not know a detail off-hand but they know how/where to look it up. This actually can be just as or more important in scenarios then intrinsic knowledge because the results returned from their sources can be truer then what they "think" the right solution is. This is that caching issue I mentioned earlier. We have a bias towards hard won information via experience that we tend to skew that way when diagnosing issues (for better mostly but sometimes not).

The key here is to not discount either knowledge base. I've seen too many "pro" or "senior" admin personality types make situations worse due to their own beliefs that they are mostly right.

Take a company like Uber for instance. They thrive on head hunting junior admins because it challenges their senior admins to be more out of the box and try new things since juniors aren't expected to have the same level of intrinsic knowledge (and thus the same biases) as senior admins do.

In consulting (where I hail from) you're often put against many different environments with varying set ups based on business needs/history on a day to day or sometimes in an hour by hour basis. So often a consultant will have "intrinsic knowledge" (tribal) on their side for the customers environment but will often only have referential on the specific details of their execution.

Let's take Mule ESB for instance. You may not know the intricacies of setting up or managing this particular enterprise serial bus system but you can understand how to read an XML file of its general "flow". Everything else is referential in nature beyond that and is a google fest.

After that you're now working with a client's email security appliance which you've never touched before. You understand the basics of an ESA (it scans incoming and outgoing email against threat rules that are updated at intervals) but not the specifics of execution.

Some of the most successful consultants and in-house engineers I know actually know only a little more then the core fundamentals of their positions. What they have in spades however is referential knowledge and an understanding how to filter for needed information in a timely manner.

So while to your point that intrinsic information is ideal to have, it's definitely not the end all be all and by relying on that solely as a metric you could very well be leaving a lot of good talent "on the table" so to speak for other companies to absorb.

Source: Ex Trainer for Apple Site Support Engineering, Ex Silicon Valley Consultant, and a bunch of other stuff. Now currently working with a successful SaaS who interfaces with every one of our clients IT departments.