I left it for Frithgar to think his post over a bit and let him respond. That post, if any, needed clarification. How many open cells do you need before running any risk?
Bees often stop collecting stores and do not cap the cells if not full. That does not mean, categorically, they have not dried it down satisfactorily; OSR is often taken before all cappings are completed or it may well granulate before extraction. Just a couple of examples.
We have the frame 'shake' test which can be applied by almost all except the most inexperienced.
Of course you can take your OSR whenever you like - but if you like remove now it will likely be crystallised. Just have be a little prescriptive to cover all situations. If the post had read as 'may' rather than 'is not' I may well have passed on quickly.
Refractometers, which in one form or another, I have used over the past 40 years, or so, are now so 'dirt cheap' (about 4 jars of honey[?]) that perhaps none should collect much honey without having one to check with if at all inexperienced - if there is any suspicion of fermentation occuring. That said, capped honey will not ferment under any normal conditions of storage.
Here we are in early August with people saying 'must harvest the honey'. I would not bother too much. I might shuffle around some frames if they looked 'iffy' (put them altogether in one super). I would pobably be leaving them on simply because they were not yet full.
If I wanted some honey desparately, I might spin out the unripened frames and then uncap and spin for finished honey, but so much hassle for a very few jars. I might just take a frame and scrape it back to the foundation and separate the wax and honey, but too much hassle. If they were not finished in the first super, by the middle of next month, I would be leaving it full for the bees, preferably. If it were full I might just extract it, and feed heavily when replacing it. But these things all need fitting in around varroa treatments and such.
With one colony the window is narrower than for me. I can move a super across to another colony for finishing, if the hive needs thymol treatment. If the season ended abruptly next week I would not be worrying unduly.
BTW, I would certainly not be considering removing frames from a hive at this time of the year if only 2/3 capped, unless I had a very good reason for so doing.
Refractometers ... are now so 'dirt cheap' (about 4 jars of honey[?]) that perhaps none should collect much honey without having one to check with if at all inexperienced