Can you source this? I'll do my best to guess, but NAD27 could be referring to things other than the data source. LCL83 clearly refers to the projection. Notable is that this projection is one that is used due to its prevalence in the military.
No evidence has been found of any type of accelerometer having being used before the early 1920s. NAD27 was obviously in 1927, and at that time there was one device on the market I know about. It's design was suited for the following applications:
“recording acceleration of
an airplane catapult, passenger elevators, aircraft shock absorbers
and to record vibrations of steam turbines, underground pipes and
forces of explosions . . .”
In other words, fairly high differences in acceleration. And this was reported in 1930, so we can expect that its accuracy had only increased since then.
Also, what defines an "anomoly". To me that word means measured gravitational amounts that differ from the prediction of the model. If that is the case, this is just a picture of all the mistakes in the round earth model.
In short: more information please. Its pretty silly for you to post this picture and expect us to know what to make of it. Where is the data? How was it gathered? What devices were used? Is this the predicted gravity or the measured?
This time don't use the google image search.