So, in California, a folding pocket knife with only the clip showing is considered "openly" carried
No. That is not a state law. But it is a standard that can be applied under local ordinances by LEO's in both Los Angeles county and city, and it only applies to knives with blades 3" long or longer. There is no state law limiting how one carries a closed, manual-opening folder. Under state law both open-carry and concealed-carry of such folders are perfectly legal, and with no limit on size.
But a fixed blade in a pocket sheath with the clip showing, part of the sheath showing, and part of the handle showing, is considered "concealed" carry?
L O effing L!
Not necessarily.
Whether or not a fixed-blade is legally considered "concealed" in California is very much a matter of intent. Members of law enforcement have a certain amount of discretion on the matter (subject to review by a judge), if they believe that it was a persons intent to try and conceal a fixed-blade from view, then they can arrest you. But again, that decision will be reviewed by a judge, who can throw out the charge.
If enough of the fixed-blade is showing that it is clear the person is carrying a knife, then they should be fine. With the normal caveat that if you cross paths with an LEO who is an ahole, or, if you give an LEO a lot of attitude, they might arrest you anyways and let the system sort the matter out.
There is also case law to protect people from being charged and convicted for carrying a concealed fixed-blade if an openly carried fixed-blade is accidentally covered by an article of clothing (like wind blowing a shirt, or a person bending down causing clothing to cover the knife), as well as other unintentional concealment from things like carrying a box or other parcel/baggage that temporarily blocks sight of the knife from view.
There are even exceptions for things like a person putting a small kitchen knife in a coat pocket for later food prep and forgetting it is there, as well as people using knives for their work, sticking it in their pocket, and then say, they go out to lunch forgetting that it is there.
Also, just because a cop can't see it doesn't make it concealed. Like if you are openly carrying a fixed-blade in a horizontal sheath across the back of your belt and you are interacting with an LEO face to face.
Again, as far as the law goes regarding concealed fixed-blades, it's all about intent.
52 year resident of California here. With more interactions with LEO's that I can remember to count.
