The view that the costumes shown in the carvings are not appropriate to the date seems to be based on a belief that baldricks were not widley worn before the revival. But is this correct?

This article suggests otherwise:

American Morris Newsletter

The article claims that the wearing of baldricks by morris dancers goes back to the 17th Century, but admittedly presents no evidence to support this. However includes a painting known as "The Dixton Harvesters" from c1720 where dancers are wearing baldricks

It also shows an 1895 photo of the Headington Quarry team. There is also a well-known photo of William Kimber wearing Headington Quarry costume, including baldricks. Of course it could be argued that the late 19th Century HQ side was itself a revival, as it had been dormant for several years before being encouraged by Percy Manning and Thomas Carter, but it was made up of former dancers and the costume was based on an 1860s photo of the earlier side (see here )

Eynsham Morris, a traditional side dating back to at least 1856, were wearing a single sash in 1901: EynshamMorris history

There is also this morris costume in the Pitt Rivers Museum. It was acquired by the museum in 1895, but came from an earlier private collection belonging to Thomas Carter. It appears to be from either Kirtlington or Headington Quarry, or possibly a mixture of both, but is certainly pre-revival.

Of course, none of this proves that the carvings are authentic, but it suggests that this cannot be ruled out simply because one of the figures is wearing baldricks.