When did S/A stop using the fancy curly type ser# style and go to the block type? That doesn't have anything to do with the low#/high# thing does it.
Are the older straight handle style bolts suspect as being weak like the low# receivers?,,same HT style perhaps..

My Sedgley has that style bolt. I like the style and everything functions so smoothly on it.

Saw a badly re-stocked '03 sporter over the weekend,,the curly style numbers & straight bolt handle. The bbl was dated '18.
Nice bore.
Had a Lyman 48 on it & 4 scope mt holes on bbl and rear receiver bridge..
Maybe should'a bought it,,but I have too many projects now.