I think the center bath is in all models 25' and above these days. The smaller units like 22' and below have the rear corner bath. The 16' has a center wet bath.
This would apply back to the 80's models, I think.
"The time is always right, to do what's right." MLK
'08 34' Classic SO, '12 Ram 2500 4X4, 6.7L Cummins.