test$ cat test.nas
nop

Foo:
global Foo

foo equ Foo
        extern foo
        call foo
test$ cat test2.nas
nop

Foo:

foo equ Foo
        extern foo
        call foo
test$ cat test3.nas
nop

Foo:

foo equ Foo
        extern foo
test$ cat test4.nas
Foo:

foo equ Foo
        extern foo
test$ cat test5.nas
nop

foo:

bar equ foo
        extern bar
test$ nasm -v
NASM version 2.16.02rc2 compiled on Oct 12 2023
test$ nasm -f obj test.nas
test.nas:7: error: label `foo' inconsistently redefined
test.nas:6: info: label `foo' originally defined here
test$ nasm -f obj test2.nas
test2.nas:6: error: label `foo' inconsistently redefined
test2.nas:5: info: label `foo' originally defined here
test$ nasm -f obj test3.nas
test3.nas:6: error: label `foo' inconsistently redefined
test3.nas:5: info: label `foo' originally defined here
test$ nasm -f obj test4.nas
test$ nasm -f obj test5.nas
test5.nas:6: error: label `bar' inconsistently redefined
test5.nas:5: info: label `bar' originally defined here
test$