Re the COOKBI edge - as far as I can tell, the edge inscription was made in sections, and the "plain" (or hyphenated) section was missed out entirely in this case, bringing the words up against each other with no gap. There is a double-size gap further round the edge, suggesting a double spacer was placed at that point in error.
No idea of relative frequency, though dealer Don Ion did a quick check of 20 or so 1969 $1 coins that he had in hand when I published the discovery and found two no-hyphens and one COOKBI, if that's any guide. It had apparently been noticed by others many years earlier, but never published to my knowledge.
Here's my provisional list of decimal varieties and errors, by denomination. It doesn't include one-off design changes (50c bicentenary edge; $2 kingfisher; 10c tuatara). It repeats many of those mentioned above, and there will doubtless be more we can add over time.
NZ Decimal Coin Varieties/Errors
1c 1971, 1980-85 circ vs. mint set; 1984-85 recut obverse on circ coins but not sets
2c ND (1967) Bahamas Mule; 1971, 1980-85 circ vs. mint set; 1984-85 recut obverse on circ coins but not sets
5c 1967 no sea; 1967 no tail triangle; 1968 no sea (reported but unconfirmed); 1971, 1980-85 circ vs. mint set; 1985 recut obverse on circ coins but not sets; 1981 Canadian 10c mule; 1999 wart nose (caused by die cracking); see R Richards Journal article (NZNJ 85, Dec 2006) for many more
10c 1971, 1980-85 circ vs. mint set; 1985 recut obverse on circ coins but not sets; 2007 to date circ vs. mint set issues; also different composition and weight of mint set coins from 2010 (Utrecht Mint strikes); ND (2011) error in proof set issue
20c 1971, 1980-85 circ vs. mint set; 1984-85 recut obverse on circ coins but not sets; 1975 struck on HK$2 blank; 2008 to date circ vs. mint set issues; also different composition and weight of mint set coins from 2010 (Utrecht Mint strikes)
50c 1967 "dot over 1"; 1985 Canadian $1 mule; 1988 recut reverse with differences in rigging/size of JB initials etc (also known on 1986?); 2009 to date circ vs. mint set issues; also different composition and weight of mint set coins from 2010 (Utrecht Mint strikes)
$1 1969 no hyphen; 1969 COOKBI (no hyphen or space); 2005 with date
Cud (top half of 5 filled); recent circ vs. mint set issues (2009 $1 with "wire rims" in proof sets); also different composition and weight of mint set coins from 2010 (Utrecht Mint strikes); 2008 "Butterfly lips" (large
Cuds caused by die cracking); 2010 "Goitre" (ditto)
$2 1998 heron beak and claws touching rim/not touching rim; recent circ vs. mint set issues; also different composition and weight of mint set coins from 2010 (Utrecht Mint strikes)
$5 2000 Solomon Islands mule