Yes, would be nice if they’d have some sort of consistency. But to be hontes? If you know thoses little bumbs and everything still works - and as in this case: works very well - I don’t care. 
Correct me if I’m wrong but products seem to have C5 since Analog Four MKI. (OT MKII shares MKI OS, keeping C4 since older release).
TBH and I work somewhat in the design field, I’m highly irritated by all this sort of negligence we learn to leave with because I stand for excellence and quality…
When ak has midi ext with 16 channels and one of them is not working because nobody take the time to actually test them,I’m irritated !
When the OT midi lfo page modifies the lfo on the audio track with the same number, I’m irritated…
And these are not higly advanced features, these are simple basic functions…
And these negligences live forever because noone cares and you always find someone who are smarter and cooler telling you that If 16 is not working, you should use 15…
In 20 years, if the world still exists, I think I should praise any manufacturer releasing a 37 keys synth if half of them actually produce sound…In a firmware update we’ll have 6 mores…Then in another a screensaver…And then the product will die like that…But I’ll expect a cool guy telling me I can still use the product because I can transpose the keybed to have acces to all the notes…
Did I mention I was highly irritated ? 
I haven’t investigated as much as other but I am reffering to different brands an their standard as mentioned by @sezare56.