For connector symbols the library developers should be looking at IEC 60617, which symbols are shown in IEEE 315A under Clause 5 that is on page 22 of the standard. The symbol developers are using the IEC 60617 (IEEE 315A, Clause 5.3.1 “Female contact”) and the IEC 60617 (IEEE 315A, Clause 5.3.2 “Male contact”). However, when these terminals/contacts are combined together in multi-contact connectors the symbol should look like IEEE 315A, Clause 5.3.4.1 “Application: engaged 4-conductors (male plug - female receptacle shown)”, the middle symbol showing mechanical connection lines.
IEEE 315A, Clause 5.3.5.1 “2-conductor (jack)” and IEEE 315A, Clause 5.3.5.3 “3-conductor (jack) with 2 break contacts (normals)…” are the symbols to use for “barrel jacks”, 3.5 mm, 2.5 mm, and 1/4" jacks for instance. Also look at IEEE 315A, Clause 5.6.1A “Coaxial plug and socket” for the proper symbols to use for coaxial connectors such as BNC, N, SMA, TNC, and RCA phono jacks. Please note that these symbols have been around for over 30 years now.
Feel free to play around with it. I would however suggest you open an issue over at github where you first show your intended changes on one symbol.
You are not allowed to change the pin positions or symbol names till we start with version 6 development as that would break backwards compatibility. (So at least these two things are fixed for the next two or three years)
I don’t have those standards available so perhaps somebody can post images of these symbols.
I am certainly one to champion the use of established and accepted standards, but connectors are one case where customary practice often trumps standardization. It’s not uncommon to depict barrel jacks, phone-plug variants, XLR and DIN-style connectors, and D-sub connectors using symbols that are visually similar to the physical connector. This aids assemblers and trouble-shooters by helping to identify the appropriate connector, as well as explain the physical pinout.