The sear you reference is a "trigger" sear, of course...found in every HK 9x firearm (semis, sear guns, factory full autos etc. etc. etc.) The unserialized full auto conversion sear can be clearly seen in pics 5 & 6, installed in the pack. It is of the variety where the trip is integral to the full auto sear...several makers made their conversion sears this way back in the day to include HTA, Ciener and David's Gun Room. The OP would need to clarify his pics, but I suspect some of the parts you question are extras or spares.
The point is with a Registered Receiver with clip-on lower, the BATF considers the unserialized full auto sear a conversion device in and of itself...and cannot be separated from the registered receiver...just like a unserialized slotted bolt can't be separated from its RR Uzi. Thus, it's permanently married to the gun...unlike a registered (Fleming, Qualified or S&H) sear which is "married" to an unregistered short bbl'd host which can be divorced, once the short bbl'd host is registered. No play on words.