dnsmasq is still not coping well with dynamic IPv6 prefixes (which are a sad reality for many users of consumer contracts), that's one of the major reasons for odhcpd.
New documentation should mention EOL versions?
That seems more confusing to me. I think the cautions to upgrade seem sufficient. Plus, not counting EOL versions (i.e. what you're using), (from the documentation's perspective) it is supported by all versions.
As a community-based affair, you can always feel free to get a Wiki account and begin editing.
You didn't get my point!
My bad. Perhaps not; because what I understood requires a time machine to accomplish.
EDIT: I should also add that the Wiki pages have a history button, any past pages may contain that era-relevant information (or lack thereof). 
Ok, I may need to test this by manually force a new address. I have a rather static address and prefix on wan. I think up to 6 months, but in 3 years I never noticed any issue. thanks for the pointer, I will have a look!
root@magiatiko:[/tmp/hosts]#cat odhcpd
2xxx:yyyy:273:7530::2 kakadu.iot kakadu
fd00:bbbb:0:30::2 kakadu.iot kakadu
# eth0.3 0001000127b5b6f6b827eb7235f3 eb7235f3 kakadu 1646299938 2 128 2xxx:yyyy:273:7530::2/128 fd00:bbbb:0:30::2/128
2zzz:www:6f:16a::3 raspi.mrv raspi
2xxx:yyyy:273:7500::3 raspi.mrv raspi
fd00:bbbb::3 raspi.mrv raspi
# eth0.4 0001000125e58871b827ebbb8a0e ebbb8a0e raspi 1646299938 3 128 2zzz:www:6f:16a::3/128 2xxx:yyyy:273:7500::3/128 fd00:bbbb::3/128
2zzz:www:6f:16a::5 rockpi.mrv rockpi
2xxx:yyyy:273:7500::5 rockpi.mrv rockpi
fd00:bbbb::5 rockpi.mrv rockpi
# eth0.4 0001000125e597e0ba4e4cc5b42c 4cc5b42c rockpi 1646299938 5 128 2zzz:www:6f:16a::5/128 2xxx:yyyy:273:7500::5/128 fd00:bbbb::5/128
2zzz:www:6f:16a::74 notino.mrv notino
2xxx:yyyy:273:7500::74 notino.mrv notino
fd00:bbbb::74 notino.mrv notino
# eth0.4 000100012833d2996c02e078680a 8841b77 notino 1646299938 74 128 2zzz:www:6f:16a::74/128 2xxx:yyyy:273:7500::74/128 fd00:bbbb::74/128
root@magiatiko:[/tmp/hosts]#ping6 rockpi.mrv
PING rockpi.mrv (2zzz:www:6f:16a::5): 56 data bytes
64 bytes from 2zzz:www:6f:16a::5: seq=0 ttl=64 time=0.652 ms
64 bytes from 2zzz:www:6f:16a::5: seq=1 ttl=64 time=0.860 ms
^C
--- rockpi.mrv ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max = 0.652/0.756/0.860 ms
Currently my system has been updated to 21.02.x but the preferred_lifetime parameter is still invalid