LGP-21 Programming manual, 3-08-ish "instruction modification and looping". talks of "computer is unaware" data is an instruction, etc.

otherwise LGP is terrible, very literalist with its coding sheets. dont seem to recognize the notes column are the program.

allied with the issue of metaphors is basic clarity and understandign, much mor eevident in the G-15

http://bitsavers.informatik.uni-stuttgart.de/pdf/bendix/g-15/G15D_Programmers_Ref_Man.pdf

which shows some grasp of context and background, situating the machine in historical context. THIS is what's lacking in most early computing, probably because  few of the implementers (or managers) had any clue.

above has sections CONCEPT OF A PROGRAM, ORG OF PROBLEM FOR MACHINE, etc. good!

though remains arcane, there is a clear semi-petaphorical, semi-literal description of data flow for the machine, registers (quoted to be clear its an abstraction) and simplified physical model of actual data, flow.