g77 does not allow DATA VAR/1/ to appear in the source code before COMMON VAR, DIMENSION VAR(10), INTEGER VAR, and so on. In general, g77 requires initialization of a variable or array to be specified after all other specifications of attributes (type, size, placement, and so on) of that variable or array are specified (though confirmation of data type is permitted).
It is possible g77 will someday allow all of this, even though it is not allowed by the FORTRAN 77 standard.
Then again, maybe it is better to have
g77 always require placement of DATA
so that it can possibly immediately write constants
to the output file, thus saving time and space.
That is, DATA A/1000000*1/ should perhaps always
be immediately writable to canonical assembler, unless it's already known
to be in a COMMON area following as-yet-uninitialized stuff,
and to do this it cannot be followed by COMMON A.