You're correct in stating that 'not guilty' doesn't equate to 'innocent', but that's only your opinion. My opinion, and I hope it's shared by others, is that 'bot guilty' is sufficient reason for me to draw the presumption of innocence. After all, these are the supposed higher echelons of the law and being not versed in legal matters, I tend to defer to their judgment.
There is a very sound basis for making a distinction between "not guilty" and "innocence".
The first is a finding of a Court (with or without a Jury) on a specific allegation and under a specific statute or tort, and supported by specified authourities in Case Law.
The second is an opinion which may be determined by the parties concerned, or other commentators or professionals, and which relates to the incident or matter which has been accused, and where the facts are tested against a reference (which may be legal statutes, tort, case law, moral codes, public opinion, media polls, friends' opinions, religious codes or practice, trade union codes or practice, scientific evidence, pressure group pronouncements or flavour-of-the-month popular opinion).
It should be easy to see that a person who is NOT innocent under a raft of opinionated tests which are not based on a test by a Court of Law might also fail to be found 'Not Guilty' by such a Court if the neccesary evidence is not forthcoming or persuasive. And equally and conversely, that a person who is demonstrably innocent in the opinion of such a raft of opinionated tests may, technically, be found to be 'Guilty' in respect of a very specific application of the evidence to some Statue or Case Law.
I have seen some heart-wrenching judgements (some in the last few weeks) in which the Court has been compelled to reach a certain decision based on the Evidence and the Statutes or Case Law but where they very obviously wished that other evidence could be forthcoming to enable them to reach another decision. It is astonishing to see senior Judges assisting claimants as far as they do in order to help them to avoid the inevitable finding of Guilt. Or to see other senior Judges (notably, Thomas LCJ) criticise Police forces for failing to comply with the basic requirements of justice, and then refusing to give judgement on the matter before them for want of evidence.
The key distinction is this:
'Innocence' is a statement of opinion, based of the available facts, and which may be determined by a wide range of people and bodies, including those involved.
'Not Guilty' is a finding of a Court of Lw, based only on the evidence presented to it and the statutes and authorities presented to it.
I hope this helps to illustrate just some of the ways in which 'Not Guilty' and 'Innocent' can differ.
[For our next session, we could look at the differences between guilt and culpability ! ]