The 'Poisson Volant' centrepiece had a very long production run; I don't know the exact dates off hand, but I'd guess at least 30 years or so. Unsurprisingly then there are differences in the bowls, i.e. some have an frog moulded integrally with the bowl, while others (much more common) have a separate, removeable frog. As regards the difference in 'pleats', I cannot say, but certainly the fish figures themselves show differences over the run, so I wouldn't be surprised if this was just due to a mould being replaced or repaired, etc. over time.
The other possibility is that the set is a marriage, i.e someone has paired up a fish figure with a replacement bowl from another maker. A photo of the set is needed really.
There certainly don't appear to be 'fakes' coming from Taiwan or manland China, in fact there'd be little value in faking this set as it's fairly common in the UK and, due to its size & weight, expensive to ship.
To the best of my knowledge there is no evidence whatsoever that Jobling made this pattern. It is not shown in the 1934, 35 or 1937 catalogues, nor is it mentioned anywhere in Baker & Crowe (The definitive text on Jobling). Whilst it is true that there is a gap in our knowldedge post 1937, I've never seen a Poisson Volant centrepiece in a typically Jobling colour. Likewise, there'd be no reason for Jobling production to be of a lesser quality, Jobling's animal figures are superbly modelled and very desireable.
Steven