Gents,
Yes, The "Vac-band" Vacumatic is most uncommon and is a very desirable pen. It is the oen from ebay last week. I suspect the cap in this style was made for limited time in 2nd quarter 1937. Pens most often turn up with "27" date codes, though barrels a smidge late do not cause great consternation. I don't sweat a "37" or even "47", and enough have turned up from the wild (particularly from overseas) that I wonder if some of the caps lingered at the factory before meeting their destined barrels.
The Vac-band cap is seen on the cover of the 1937 Parker catalogue (undated paper, iirc, other than by year) and in the first of the 2nd Generation Vacumatic ads (showing pens such as Maxima, Major), those ads appearing around August 1937, noting that manufacture and advertising can have some lag time.
The pen indeed is from ebay last week. It has a later clip as it should have a plain feather clip, but this is a readily swappable part (unlike clips from many other companies).
The Sheaffer is interesting too.
regards
david