[Mr70]

That's because it was redundant when the now new RPO Z15 was ordered on the 1970 Chevelle,so they didn't mention the RPO B22 SS door emblems on the assembly instructions.
Z25 Chevelles had them automatically called out on their BS,because it was one of the base Super Sport ornaments.But in order to get a Z15 equipped Chevelle,(be it LS-5 or 6),you had to order the Z25 equipment first.So generally speaking those emblems were included when you upgraded to a Z15,but it wasn't noted on their BS and that lil glitch was why.
Chevrolet notified assemblers to start including the "SS" door emblems on all Chevelle Super Sports,regardless of Z25 or Z15,but a few didn't quite get the memo.
Having a Z15 specifically callout "B22" on the BS is the real anamoly.