Bootloaders not seeing Endeavour installed into new partition

Situation: a dozen old intel-chip Macs…

  1. Boot into Mac Recovery Partition; csrutil-disable in Terminal to disable secureboot.
  2. Created new partitions on the drives (leaving existing OSes intact).
  3. Install Endeavour into the new partition; appears to be successful.

Problem: Endeavour does not appear in the bootoader (whether OEM existing, or after subsequently installing rEFInd or OCLP). There isn’t any issue when clean-installing, i.e., Endeavour’s partition appears as a generic-icon EFI bootable drive and subsequently reinstalling a MacOS into a new partition doesn’t disturb anything - but my goal is to add Endeavour to new, rearward partitions on the drives, and for the systems to be managed by an icon-“pretty” bootloader…

Any suggestions?