It's a little of both. The First Class seats are definitely a "place holder" map in case their is an aircraft swap. The economy plus seats in 12-15 are a seat map for a 737-9 Version 3.

Yes, I suppose you could get kicked to the back of the bus if a V3 changed to a V1/V2 at the time of your flight.

I had the opposite experience a few weeks ago. When I checked in at T-24, I saw my aircraft had swapped to a V3 and moved up from Row 35B to 14C. Deep middle to a forward aisle was a score for me