JB105 you will have to reconcider your statement.Replacement notes of all types (asterick,letter X or inserts) were not put in there matching prefix.
For instance the bird series $2 notes, all Bonin notes were replaced with either EBX or BRX and there are no Bonin EB or BR denomination letters.BRX would have been used as replacements in CBH,I,J,K.
It's like modern inserts, finding an FED prefix in a FEB bundle.
So if a replacement was used for S/R test notes they would not have to be *S/R.