GREAT POST! Don't we ALL wish the 1850 Johnston County census had township names instead of numbers! You didn't give a name of a person. I can tell you what I have done in the past - I look up the family in the 1860 census - I know that one has the whole lot bunched together BUT it does give post offices! I've been able to use that to help me.
Wouldn't it be wonderfully helpful for the SMITHFIELD HERITAGE CENTER to PUBLISH on their Historic Population page a chart that shows the corresponding township(s) for those 15 unidentified numbered districts. In fact, I am still puzzled that site hasn't done any reference work for POPULATION in JOHNSTON COUNTY BEFORE 1870! Considering Johnston began in 1740s, the center has a gaping hole encompassing 124 years!
Also, I see your post has a HOLLIMAN moniker. My work involves this family, specifically Nancy Holliman who married Edward Sasser Jr. Her sister Polly Jane, married Edward Sasser's brother William Edward. It gets quite confusing. The gals' dad was Ransom Hollomon. One of the death certificates calls him "Ronnie", possibly a nickname for Ransom... The Mom was Hannah Toler, I believe. Still very early with me and this line!
Also for what's it's worth - my project is jumping back and forth between Fork township in Wayne and Beulah down to Boon Hill in Johnston at the moment and has at times gone off to Wilson, Wake, Harnett, Lenoir, and Sampson counties. Not sure if any of this will help you at all.
Figured I would try.
I hope it does.