I believe (but am not sure) that the Flandria teambikes, like the one Maertens rode, were really De Rosa frames. There was a 70s Flandria (with all the right colours) on kapaza.be where the seller claimed it was Maertens training bike. This bike looked like it was accidentally but partially covered in some black paint, looked like it had been slung in a ditch and dragged out again. Closer inspection revealed an Ishiwata 022 tubing decal. I can't believe Maertens would have used that, with all due respect to Ishiwata of course.

Probably just a period team replica bike.