Welcome to the forum, mgjsmith.
Octoinks are respected here in the forum as is your Canon Pro 100s.
Sounds like you have done a great job flushing your cartridges. As you have seen, not every cartridge sponge may flush to white. It is not essential to flush all the cartridge to white or even to flush them at all (MAJOR EXCEPTION BELOW) unless you want the best color fidelity from your Octoinks from the start. If you are going to be making your own printer profiles then you would want to flush all the cartridges so no OEM inks remain, or, you would wait a refill or two before making the profile to dilute / use up the OEM ink remaining mixed into the Octoinks.
However, you do not need to flush cartridges at all
EXCEPT FOR THE YELLOW.
Canon OEM ink for the Pro 100 line is known to gum up and become a clogging sludge known as YELLO GELLO (so named by our Moderator The Hat) that stops ink flow through and out of the cartridge (ink starvation) and clogging up nozzles in the print head. This occurs when OEM Yellow ink is exposed to enough water (maybe other substances). If refilling, this Yello Gello may form after 4-5 refills if the OEM cartridge is not sufficiently flushed and cleaned before using aftermarket ink.
To make sure you do not experience Yello Gello, either buy a Yello CLI-8 cartridge and swap the chip from your Yellow CLI-42 cartridge OR flush the Yellow cartridge with Windex with Ammonium D (original formula) or similar product, till the sponge is clean and then flush with water. That's all.
Here is The Hat's OEM Yellow cartridge cleaning recommendation. (You do not need to do the step with "pharmacist's solution" which is for reconditioning the sponge)
https://www.printerknowledge.com/th...estions-on-cli-251-printers.11587/#post-97508