From over on The TCCCF Butt plates section:
Post WWII
When WWII ended Springfield Armory assumed control of the U.S. Carbine program and parts inventory. Replacement stock production continued well after WWII. Buttplates used were obtained from surplus/replacements made during WWII that had yet to be used. Springfield Armory is known to have manufactured buttplates post WWII using equipment left over from at least one subcontractor. Springfield Armory also packaged surplus used and new buttplates for long term storage. A buttplate covered in grease and packaged for long term storage may or may not be "new and unused".
1- Is it possible 'The left over equipment from one sub-contractor' Had the missing Dot pattern?
2- Many missing Dot plates in NOS condition were left over and repacked?
3- Some of both?
4- Just swinging at curve balls
But I do recall Ricca saying he un-wrapped SA marked packs with all the plates missing the Dot. Positive on that.