embarrassingly late, but if of any use there here goes...........

Kew pictures attached for these four lidded pots/jars - regret I've rather lost the plot and not sure now if we resolved the meaning of 'F E Co.' or not. It's the first of these four Rds. that started this thread, and the original blue-print drawing for 563868 doesn't make any reference to, or show physically, that this particular Rd. included a plain oval space as part of the design - as in fact does appear on the jar shown by Fred.
However, the drawing for Rd. 563870 with the slanting style of decoration does indicate this oval type of window was available, and bearing in mind all four items appear to have been intended for some form of bottling or pickling of fruit etc., then perhaps it was intended they all had provision for a clear window, on which you could stick your id label .... raspberries, gooseberries etc. with relevant date.
Unfortunately, one picture will flip over to the following post, and if the wording re the 'plain space for label' appears less than legible........... it reads......
"Oval represents plain space left in the design for label as per small sketch at foot which shows other side of jar. The jar is circular in plan"