Hi Frank - My practical experience of bottle works is very limited. As a glass technology student I worked at Portland for eight weeks in 1947 and, apart from brief visits to several others, that was it.
I knew of Monish machines, of course, but I've never seen one. My report on Portland has survived (there's not much else from those days) and I see that they had six Lynch Model R machines, three O'Neill models 42 and 44, three Roirants and two Forster hand-operated machines (these latter noted as out of use). I only saw Lynch and O'Neill machines working. One of the O'Neills was brand new but, in industry terms, the Model R Lynchs were obsolescent. Their successor, the Lynch 10 was rapidly becoming the standard machine in the UK but it itself was later to be succeeded by the seemingly everlasting I.S. series which you mention.
In the 1960s and early 1970s, when I was at Jobling, a surviving Lynch 10 could still be seen in use for only a few weeks per annum serving the presumably dying market for glass (Pyrex) feeding bottles.
There are lots of drawings and descriptions of these (apart from the Forster) and others in "Glass Machines" , edited by W. Giegerich and W. Trier, translated from the German and published by Springer-Verlag in 1969. Title of original edition "Glasmaschinen".
You are correct that many of the numbers seen on bottles will be simply internal things like mould numbers. I can only remember one or two company logos. Portland was (I think) P in a circle, Rockware was R in a circle and Beatson Clarke (Yorkshire) was a double arrow thing a bit like the old British Rail logo. Somewhere in the past I have seen a list of these things and it must exist somewhere!!
Good luck!
Adam
P.S. My wife has just told me that she has heard of musical movements in the bottom of Drambuie bottles. No further info, I'm afraid.