Correct on the 40, means it's somewhere around 40'. The 23 denotes the floor plan. To find that you need the brochure for that model year.
Ours is a 4090, actually it's closer to 41' than 40'. Even though the 90 on our rig denotes the floor plan we had two pocket doors and two walls removed and a vanity from another model added. To actually see what ours looks like you'd need to look at a later year as Newmar must have liked the change and offered it a year or so later.
2009 45' Magna 630 w/Cummins ISX 650 HP/1950 Lbs Ft
Charter Good Sam Lifetime Member, FMCA, SKP
RV'ing since 1957, NRA Benefactor Life, towing '14 Jeep JKU Dragon Edition