There is no single rule about how a compiler stores data in the output files it produces.
Data can be stored in a “constant” section.
Data can be built into the “immediate” operands of instructions, in which data is encoded in various fields of the bits that encode an instruction.
Data can be computed from other data by instructions generated by the compiler.
I suspect the case where you see “Nanc” in one place and “y” in another is the compiler using a load instruction (may be written with “mov”) that loads the bytes forming “Nanc” as an immediate operand and another load instruction that loads the bytes forming “y” with a trailing null character, along with other instructions to store the loaded data on the stack and pass its address to printf.
You have not provided enough information to diagnose the g++ case: You did not name the compiler or its version number or provide any part of the generated output.