Good points again, dog. IMO, many caches were relocated, augmented and brandished with new cover stories in the 1930s, for various reasons. In doing so, IMO, the need for sentinels was eliminated because of the new caches' locations (very restricted access for snoops) and most importantly, because of the bogus clues and signs created to send would be searchers in wrong directions.
Your observation re surveyors is also correct, IMO. However, be careful about the old marked stones you find. Remember, before the days of rebar and alcaps, land surveyors frequently marked property corners with chiseled stones. In fact, right now, my searching partner and I are volunteering to flag property lines for a bunch of patented mining claims newly acquired by a monastery in the hills above Silver City. The original corner stones seem like "treasure code" to many - for example, "1211 - 4 - 3" carved on sides of a prominent rock. This is not a treasure clue, but the legal corner of Mineral Survey 1211, corner 4 of one claim and corner 3 of another. Same goes for mysterious X's found carved here and there - usually some sort of control point an old surveyor used. These discoveries can be researched if you care to take the time.
That said, think about this. If you wanted to cache valuables in some obscure site, who better to locate it exactly for you than a land surveyor? There are many ways to do this using the Township grids in use all over America (thanks to Thomas Jefferson, who invented the system).