The latter could simply be mediocre work contemporary with the bottle; or some dealer trying to raise the bottle's value in the 1960s to 1990s, when plain Jet bottles from the 18th & early 19th C. weren't valued as well as they are now.
Dear Joey,
That thought had crossed my mind too. But then I re-looked at the subject matter and overall style of the decoration on Mat's bottle, and think the work is probably near contemporary with the bottle. I say "near contemporary" because I understand that drawing with the iron brush was a popular pursuit of literati as an outlet for their artistic aspirations, which was regrettably mediocre at times. The "blank" bottles would have been produced for that purpose, rather like the blanks created for inside painting. In fact I wonder if the undecorated jet bottles we treasure today are simply the ones which escaped the iron brush.
Another reason for thinking the decoration is not modern is because the narrow side(s) have calligraphy. Nobody trying to raise the bottle's value in the 1960s to 1990s would have bothered covering both main sides AND the narrow sides too. Conversely, if the calligraphy is old (which to my eye appears so) why would the literatus place it on the narrow sides and leave the two main sides blank?
It is more likely that the literatus drew his scenes on the two main sides, then decided to inscribe a few lines of calligraphy, and used the only space left!
All best,
Tom