However we were told we would need a slide with the larger number of cocking serrations for the pistol.
Yes, like I said. The later variation had MORE slide serrations which were also thinner. You can see it in my 32 photo. The earlier type is probably more common since the 32 was introduced much later in the guns production and only 10k 32s were made. Now of course, there were many later model 380s made as well, but I surmise that the 9 slide serration guns were a higher production.
These seemed to sell well at onset but then the sales tapered off for many reasons. And to think, the 51 was less than a Colt 1903 at the time and yet people still paid for the horsey. Nothing against the Colt but it is to me less special. Imagine the 51 plus .45 = 53