Let's not confuse Arnold (Rivarossi) and Rapido.
I know Arnold had a BOGO sale but I don't think Rapido did any such thing.
Well, Arnold/Rivarossi merger is also old history. Nowadays it is Hornby/Arnold. Hornby (in Spain) is the parent company now that is just using the Arnold brand name.
The original German Arnold company used the name
rapido for their N scale offerings. The current Canadian manufacturer
Rapido Trains isn't related to Arnold/Rivarossi/Hornby companies at all. Before Rapido Trains came along, the original German Arnold company never sold any models using just the
rapido name. They were always
Arnold rapido. The "rapido" branding was always all lower-case letters and it hasn't' been using by Arnold (or any of its future reincarnations) since IIRC the 1980s, or even earlier.