If I can put it a simpler way, we made absolutely clear to our new employers, "Although this will be day one for us with you; in all respects, you need to treat us exactly as if we have been here for 8 years". So far as I can tell, thats the way it works, in a nutshell.
Nearly.
"In all respects, you need to treat us exactly as we have been for 8 years" is more correct. That's TUPE.