Yes, the entry can be left as it is.
Actually, googling around, it’s OK in fact to talk about information being “summarised
in a plot” (“sum up” being the wrong register, I’d say). See e.g. para. beginning
“This information can be summarised in a plot of the variances” on page 5 of http://people.maths.ox.ac.uk/richardsonm/Sign...
and see Figs. 3 and 4 for different examples of a “plot”.Maybe "plot" wouldn't have been used generally to mean "graph" a few years ago in the UK?
No, it’s been around for some time. I can’t remember how long I’ve been aware of it, but the 1989 version of the OED lists the “graph” meaning in its entry for “plot”:
d. A diagram showing the relation between two variable quantities each measured along one of a pair of axes usu. at right angles; = GRAPH n.1 2.
It’s not that the BE dictionaries you consulted are out of date, but rather that they’re not exactly strong on things technical. The Concise Oxford isn’t too bad (nor is Chambers incidentally), but presumably terms that the editors (all arts graduates perhaps? SCNR;-)) consider a bit specialised inevitably have to be left out or the dictionary would no longer be “concise”. The Longman, I notice, is an Advanced Learner’s Dictionary, and seems pretty useless on technical/scientific English in general, as are the Oxford and Cambridge Advanced Learner’s dicts. I looked up “rad”, for instance, in the Longman, assuming I’d find something about radiation dose or at the very least something about plumber-speak for radiator, but this is all it gives:
exciting or interesting:
Have you guys seen Wendy's new place? It's so rad.http://www.ldoceonline.com/dictionary/rad
CALD and OALD definitions of “rad” are confined to the same meaning as that given in the Longman.
So, it seems to me you could be wasting your time looking for anything even vaguely technical in the Longman, or for that matter CALD or OALD. Hope that helps for future reference:-).