It does and it doesn't
Unfortunately, my experience is a bit more...recent
However, some basics apply, even to that era when such things were unregulated and free form-
1) Threat assessment: Know Thy Enemy. Anyone doing a protective detail will either receive or do advance work to ascertain the nature, strength, disposition, etc. of threats to their principle (or client, to use the old-school vernacular). These days we assign members of our detail to do the advance work, planning out routes, interviewing and doing backgrounds on employees of venues the principle will visit that may have close contact with the principle, sat-mapping alternative and emergency evacuation routes, getting current crime briefings from local LE, etc. In your case, it could be as simple as paying the paperboy on the corner near the threat's location to slip him info
2) Situational awareness: Know Thy Environment. This is a general practice of being acutely aware of your environment and the people in it. Know where exits are, monitor entrances, watch people, especially body language, dress, hands, etc. A guy wearing a jacket in 90 degree heat- armed. Someone's hands disappearing into loose clothing- potentially about to pull a weapon, be ready to move. Guy on a cell phone holding it to the side with his finger on or near the keypad, watching you rather than the phone- potentially about to pop an IED or EFP by remote. Look for collections of cigarette butts of the same type in an area that is concealed and has a line of sight on your client's location, watch mannerisms, people sweating in the cold without exertion, someone walking with one hand staying by their side rather than moving, etc.
3) Have a plan: Know Thy Way Out. You should not only have multiple routes to the venue(s) your client intends to visit, you should have not one, but three evacuation routes and evac plans in case things go south. These plans should not be spur of the moment ones, but thought out ahead of time. He should be playing out scenarios in his head the whole time- "Okay, if we have a fire, I will secure my client and head for exit 1, unless that is blocked, then we will head to exit 2.... if that guy with the heavy overcoat who looks mafia-like is a hitter and draws, I need to secure my client behind me and withdraw under covering fire- accounting for every round I fire, don't want any civies hit- and back towards exit 1, unless it is under fire, blocked, or compromised, in which case, exit 2.... if a demon from the pits of Azagoth crawls out of that cooking pot in the kitchen because someone cast runes at me on a napkin..."
Those basics are the same no matter what. When you get into modern executive or diplomatic details, it gets a LOT more complicated, but back then there wasn't a lot of regulation, specialized training, or the like, so it allows for more adaptability as an author.
Hope some of that helps
