Correct, it did not show at (10.11.6) Mac App Store Updates at all.
Codebook was visible from Purchased, but it showed it there with Open -button not Update -button. Similarly when I searched with name and opened software product page it was also showing Open -button. I tried if reboot helps before writing etc., but did not remember to check if signing out App Store would solve the issue which it apparently did.
After your advise I signed out from App Store, rebooted and signed back again. Then it took fairly long time checking updates and before Codebook update showed up. Once it was there update went fine. I’ve already updated my devices and crosschecked that wifi-sync works fine too.
I’ve used Macs since 2004 and some minor annoyances sure, but I don’t remember if this kind of stuck update did happen to me earlier. Other minor annoyances sure have been, but not that much lately.
Anyway, thanks a lot for help. Codebook is great and so is your attitude towards customers.