Hi mocore:
My comments are largely based on limited experience on one of
my test machines configured as follows:
sda1 ntfs Windows 7 primary partition
sda2 ext4 1 GB boot partition primary partition
sda3 ext4 a Linux distro primary partition
sda4 extended partition
sda5 ext4 a Linux distro logical partition
sda6 ext4 a Linux distro logical partition
sda7 ext4 Bodhi 4.3.1 logical partition
sda8 swap logical partition
Bodhi 4.3.1 is installed with sda2 as its boot partition, sda7 as its / (root) partition.
Bodhi, as a Ubuntu derivative, has the update-grub command available to update
the current chain list of distros in sda2 after any new installations in the other partitions.
I am not nearly as adept as polikuo is on maintaining the menu entries in the sda2
boot partition, so I rely on the update-grub command in Bodhi to do that.
At one point, I did a straight-forward frugal install of CorePlus 8.2.1 in sda3,
and found it accessible with Plop or Super Grub Version 2.02s3 directly.
At another time, I did the frugal install followed by the grub-0.97 install as initially
described in this post into sda6. I then invoked Bodhi, and ran update-grub,
and expected to be able to boot CorePlus up from Plop accessing sda2, but it
didn't work. Somehow, the chaining from sda2 to sda6 didn't work.
I was able to boot into sda6 directly with Super Grub and bring CorePlus up o.k.
Throughout all this, the MBR is untouched, and with no external boot loader
employed, the machine boots up in Windows 7.
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(My intended use of CorePlus is for a very old, small laptop with only an sda1 root
partition and a sda2 swap partition, but while I'm finding my way on my other machines,
I've run into these boot-up intricacies).
Hope this now makes more sense .......
Len E.