kern/57081: ZFS pool rolled back two years, all data lost since.

[roy%marples.name@localhost]

>Number:         57081
>Category:       kern
>Synopsis:       ZFS pool rolled back two years, all data lost since.
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Nov 11 09:40:00 +0000 2022
>Originator:     Roy Marples
>Release:        9.99.106
>Organization:
>Environment:
# uname -a
NetBSD cube.marples.name 9.99.106 NetBSD 9.99.106 (GENERIC) #3: Thu Nov 10 12:45:17 GMT 2022  roy@cube:/usr/obj/sys/arch/amd64/compile.amd64/GENERIC amd64
>Description:
cube# zpool history | tail -n 10
2020-10-18.14:15:39 zpool import -f -N rpool
2020-10-18.14:16:22 zpool scrub rpool
2020-10-18.15:20:25 zfs send -Rv -i rpool@snapi rpool@snap
2020-10-18.16:31:12 zpool import -f -N rpool
2020-10-18.16:49:30 zpool import -f -N rpool
2020-10-18.16:54:57 zpool import -f -N rpool
2022-11-10.14:21:38 zpool import -f -N rpool
2022-11-10.14:28:55 zpool import -f -N rpool
2022-11-11.09:07:58 zpool import -f -N rpoolv

As you can see there are a few years missing and the mounts on the rpool look like it was about 2 years ago - loads of things missing.
>How-To-Repeat:
Uknown, unwilling to experiment in the thin hope I can recover the data.

What I did was upgrade from 9.99.93 to 99.99.106. Installed everything as usual but when I booted into the new kernel it failed to load the solaris or zfs modules.
In single user `modload solaris` fails. I had to navigate to the actual directory where it was stored and do `modload ./solaris.kmod`

[   168.867653] DEBUG: module: Loading module from /stand/amd64/9.99.106/modules/solaris/solaris.kmod
[   168.867653] DEBUG: module: Cannot load kernel object `solaris' error=2
[   316.886565] DEBUG: module: Loading module from /stand/amd64/9.99.106/modules/solaris.kmod/solaris.kmod.kmod
[   316.886565] DEBUG: module: Cannot load kernel object `solaris.kmod' error=2
[   336.136424] DEBUG: module: Loading module from ./solaris.kmod
[   336.146460] DEBUG: module: Loading plist from ./solaris.plist
[   336.146460] DEBUG: module: plist load returned error 2 for `./solaris.kmod'
[   336.146460] DEBUG: module: module `solaris' loaded successfully
[   382.106086] DEBUG: module: Loading module from /stand/amd64/9.99.106/modules/zfs.kmod/zfs.kmod.kmod
[   382.106086] DEBUG: module: Cannot load kernel object `zfs.kmod' error=2
[   391.146019] DEBUG: module: Loading module from ./zfs
[   391.146019] DEBUG: module: Cannot load kernel object `./zfs' error=2
[   400.465951] DEBUG: module: Loading module from ./zfs.kmod
[   400.465951] DEBUG: module: Loading plist from ./zfs.plist
[   400.465951] DEBUG: module: plist load returned error 2 for `./zfs.kmod'
[   400.465951] DEBUG: module: dependent module `solaris' already loaded
[   400.505950] ZFS filesystem version: 5
[   400.505950] DEBUG: module: module `zfs' loaded successfully

No actual ZFS errors were reported, but the disks remained in this rolled back state.

Any advice on how to recover, welcome :)
>Fix: