Well I figured I'd update this thread, recently an old stock SR set came up for a great deal here on the forum, and they were quickly snapped up;
At the same time another later made (same number) set had been on eBay for about a month, and those too recently sold.
You can see between the two that the way they were manufactured DID indeed change.
The early ones have (as previously shown in this discussion) the part number stamped up on the small collar of the pipe, while the later ones have the part number stamped on the top rear edge.
The early ones are also a mandrel type bend (I don't know what it would be called; the pipe diameter does not reduce), while the later ones have a reduction in the bend.
The following images are of the older stock SR tips:
