Mountdord, those definitions are really unhelpful.
Yes, in selective area, both schools where you have to pass the exam and the schools you get when you don't pass the exam could theoretically both have some children of all abilities in them - however, they wouldn't be comprehensives.
Comprehensive schools only exist in areas where all state schools take in regardless of ability. Most countries have this. There will still be some schools with very few low ability children and some with absolutely loads, which will largely be due to where the schools are located and so who goes there. However, they are all comprehensives because they admit irregardless of ability.
In areas where there are grammars, you can only get a place if you pass the test. This means the grammars are not comprehensive, even if somehow some low ability children creep in, because they are not admitting absolutely everyone regardless of ability - you have to pass a test. And the consequence is then felt in the other schools where you do t have to pass a test - the secondary moderns,nor Upper schools or High schools or whatever you wish to call them. In areas where everyone takes the 11+ (like Bucks, where it's an opt out, rather than opt in, so the majority do sit it) children are stated to be 'grammar qualified' or 'upper qualified' - they deliberately don't say failed, but try to make a positive of both types of school - which is a good thing. Some of the Grammar qualified children may opt for an upper or secondary modern school, but the vast vast majority who are grammar qualified go for a grammar. If 25% qualify for grammars, 75% don't and the upper or secondary moderns don't have the full 100% range of ability so they are not Comps. They may be very good schools and may achieve at a higher level than some Comps, but they are not Comps. They may have cleverer children than some Comps where there is no selection in those particular areas, but they are not Comps.
Comps only exist in areas where none of the state schools in the area select by ability.
If you want to call the Sec Moderns or Uppers Comps, then you will also have to call the Grammars Comps too.
All of this jargon discussing comes about because people feel it is acceptable to say their child goes to a Comp, but not that they go to a Sec Modern or Upper or High school or whatever term is used. It is because when you go to a Comp, you haven't been excluded from a selective school by not passing an exam. However, if you go to a Sec Modern or Upper, you usually are there because you CANNOT go to the alternative, becaue you either didn't pass the exam or you chose not to sit it - so you are not qualified to be at that school. That is the reality, and somehow people like to use the word Comp to avoid recognising that reality.
So, regarding the great non-Grammars in Kent, of which there are a number, most of the children in them are not qualified to attend the Grammars. This maybe because their parents chose not to put them through the 11+ process, but just to go for the good non-grammar....absolutely fine, but it means they are not grammar qualified. And the other group are those who did sit the 11+ but didn't pass it and so are not grammar qualified.
In a true Comp area, no-one is absent from a school because they are not academically qualified. You might not get in because you don't live near enough or have a sibling or meet the religious criteria.....but it will never be because you haven't passed an academic test.
Ask any teacher in a full grammar area - they will never call the non-grammars Comps. and actually you will find they often use the term Sec Modern amongst themselves, even if it isn't the official name of the school - because in fully selective areas, schools are grammar or sec modern.