I guess this is my fault, since the wording for OB 11C2-5 was adapted from one of my suggestions, and 11C5 in particular is almost word-for-word. You can probably still find the original post in the rgb archives somewhere.
For reference, here is the section on 1♦
from the 2005 Orange Book.
12.2.3 1♦ opening may be played as any one of the following.
(a) natural, not forcing
(b) balanced, forcing or not
(c ) natural or balanced, forcing or not
(d) natural 1♣ opening with no suit longer than clubs, forcing or not
(e) natural or a natural 1♣ opening with no suit longer than clubs, forcing or not
(f) natural or balanced or natural 1♣ opening with no suit longer than clubs, forcing or not
Note – additional distributional constraints (e.g. no four card major) are permitted as treatments – see 9.4.2 [EB August 2001]
Note – in options (c ), (e) and (f), it is permitted to play the natural element as canapé, provided that the suit contains at least 4 cards, i.e.
(as an alternative to the balanced and ♣ hand-types) the hand may be one-suited with ♦s, or two-suited with ♦s the shorter of the two
suits. Unless the hand contains both minors, it is not permitted to play the natural element as only potentially canapé, where there is
ambiguity as to the relative lengths of the suits if the hand is two-suited. [EB February 2005, p34]
opening was exactly analogous at Level 3; but only (a)-(c ) applied at Level 2 so it's easier to understand the 1♦
opening where everything was in one place.)
I didn't like this old regulation - partly because it seemed that (a)-(f) weren't really distinct choices and ought to be combined into a single possibility; and partly because it relied on knowing exactly what "natural" meant. For example a MIDMAC 1♣
opening denies a 5-card major but shows at least one 4-card major. All such hands are either balanced, natural clubs or natural diamonds. But if a "natural" option always has a second suit, is that really natural? I wasn't sure. Hence OB 11C2/4, which attempts to explain exactly what shapes you can and can't include in your minor openings - any subset of the allowed hands is permitted.
That rewrite excluded canape openings, which would therefore have to be dealt with separately. But that didn't seem so bad, because it would be a chance to clear up the rather convoluted paragraph at the end of the old section 12.2.3. The new OB 11C5 was meant to be a direct translation of that paragraph.
OK, so what happened to the "natural opening in the other minor" possibility? Well, initially it was just an oversight. In fact the original version didn't have option (d). But then I played against a pair opening 1♦
with both minors either way round and realised I'd forgotten about that. By this time the new version was already in a draft and I had to rather sheepishly go back and ask for my suggestion to be changed. Obviously the whole "natural opening in the other minor" option could have been added back in but I don't think anyone believed that anyone would be playing such a thing. To be honest I wouldn't have thought that canape in one suit and non-canape in the other suit was playable; that might have been part of the reason I'd overlooked the possibility originally. (Perhaps if it's always single-suited it's not so bad, but I think it would be more normal (and better) to open 2m with that.) Also, arguably, the only reason it had been allowed in the first place was because of the rather awkward merging of the canape and non-canape regulations for 1-of-a-minor, and if a regulation for canape openings had been written from scratch the possibility of having a non-canape hand with the other minor would never have been in there in the first place. So, with no-one likely to be playing it, it seemed reasonable to tidy things up by leaving it out.
I suspect that if anyone had complained when the draft OB was produced that this change would make their system illegal, then it might have been added back in; certainly this happened in a couple of other places in the regulations at that time.