Darn, indeed. Anyway - when you said: "2. tried w10 ISO 1709 Clean install" - it can't be true.
(1) An ISO cannot do a clean install. It must be burnt to DVD & booted through the UEFI boot choices menu to do a clean install. (Or, an Installation USB drive can be booted.) Then, you must wipe the SSD to unallocated space, & install into
that. In that case, everything would be new - beautiful new partitions & a brand new BCD. (Edit:
However, I would unplug the HDD first. The clone parent doesn't belong, & its partitions may have an ill affect on the new BCD.)
(2) If you don't wipe the existing partitions off the SSD, but only make a new area of unallocated space, & install into that - it is a
dual boot. The v.1709 Windows partition would be clean & it would contain a folder that holds its own Recovery Environment.
But the v.1511 EFI (system) partition would be kept, & its BCD would be shared with v.1709. The existing Recovery Partition still belongs to v.1511.
(3) If you open an ISO in File Explorer, click its Setup.exe, & directed it to install into the v.1511 Windows partition - that is an upgrade install. It is the same as if you took the upgrade through Windows Update. You end up with v.1709,
& a new v.1709 Recovery Partition. The v.1511 Recovery Partition gets emptied but is not deleted. And the EFI (system) partition is taken over by v.1709, but the BCD is not fresh. It is altered but carries junk entries from v.1511 days.