My personal take on this is that G1/G2 is a poem about creation. It contains information from the strict scientific truth, it has to because the same God created the science and inspired the poem. It also contains some dead giveaways that it's intended to be read as a poem. It has a parallelism to its structure, which makes me think it is intended to be recited. It also has days before the coming of the sun.
Because it only contains part of the technical information I think it's an unjustifiable move to try to deduce strict scientific information from the G1/G2 account.
The point is that being a poem it is a true statement of the poet's emotional reaction to the idea of creation. However being a poem that's thousands of years old we get it shorn of its cultural context, and too easily force it into the wrong category.
To explain this I hope you'll indulge my quoting from my own Science Fiction:
Hours later she began to wander into a bleary, partial wakefulness. She'd tried to sleep in an acceleration seat—something almost impossible to do comfortably. She winced as she realised what had happened—she'd tried to turn over in her sleep, in a seat designed to hold the occupant firmly in one position with their back to the thrust line—and the seat, with its harness, had won.
She stretched, trying to ease the stiffness, and her left hand caught the stick, deflecting it fully forwards.
The lurch as the gyros kicked in, pitching the ship nose down in response to her unplanned command, jerked her rudely and fully awake.
As the ship slowly turned, the entire span of the galaxy came into view, filling the glass from edge to edge, but now she was fifteen thousand light years above the great disk, and seeing the spiral arms laid out in their majesty as a vast diamond tapestry in front of her.
The endless curving arches of stars burned on, ageless and silent in the darkness, returning to the unwinking glory of the complex, terrible core. Somewhere, out there, in that stark, cold beauty was a region whose diameter was barely one hundredth of the whole galaxy, which was everything that every human had known. Out there, in a space that she could blot out with her thumb, on five hundred worlds, every man, woman and child, save her, lived and died, and rejoiced and mourned, and fought and made peace. And still the awful majesty of the stars burned on, tearing her soul apart with their unchanging loveliness, in the depths of their silence speaking the truths she couldn't bear to hear.
She'd been running, running from herself. She'd lost her temper with Alan, Alan was dead, and there was nobody else to blame. Life wasn't a game any more.
That—and nothing else—was what she'd to learn to live with, the knowledge she'd take to bed every night, the truth that she'd wake up with each morning.
She could run if she chose, she could try to hide—but the stars would always be there to remind her. Or she could turn back and, one day at a time, learn to live again.
She sat for long minutes, drinking in the beauty of the stars, filling her soul to overflowing with their silent joy. Then she shook her head.
‘I can run from myself,’ she said out loud, ‘but I can't run from the stars—not any more.’
Now that's not intended to be a strict scientific description of the Milky Way, but it is informed by my knowledge of astronomy. In fact you'll spot that I have taken one liberty with the truth, the galaxy is not "unchanging", but on the time scale that Jane is using it doesn't appear to change.
The point is that if a modern writer can write a poetic description of something, and know it to be distinct from a strictly factual one, then surely the authors of G1/G2 could do the same.