There is no difference, it appears that the new codes began as the Welk started to sell points based, rather than weeks based units.
The Villas on the Green are a seperate section of the resort on the same property. VLW & VL2. Those units are newer, and have a completely different floorplan (lockoffs). Our personal preference for our family with 2 adults and 2 kids are the big open 2 bedroom units in the Welk Resort Villas section. The Villas on the Green are a bit fancier, but more cut up because the larger and smaller side of the lockoff have a kitchen and living room area. So spaces are duplicated and smaller on each side.
2 bedroom units can be harder to find at Villas on the Green because many lock-off when they deposit, but the Welk Resort Villas are only 2 bedroom units.