The ones w/o the letter are earlier. When the numbering system reached the end of the normal sequence, they began prefixing with a letter, starting with A and so on. Steve may have some input on this as he is researching reproducer production.
Thanks, Bill, here is what I have on DD serial numbers and letter codes.
Edison reproducers have letters before the serial numbers: LG is long play EM is one with Duncan stop LD is the Dance no letters & A to F Regular DD reproducer Edison started out with just numbers and when he got so high (999999) he started over with an A and worked his way up. NS before the serial number Edisonic NS after the serial number Converted Edisonic I know of two Dance that were converted to Edisonics and have a serial number like this LD 4675 NS. Edison never wasted. You could trade in a regular reproducer and $6.75 and save $12.75 on an Edisonic, Edison then modified the head with a larger limit loop and installed the heavy weight and thicker diaphragm on it.
With regards to the stylus bars I have seen letters up to a T and I am not sure what they were for unless it was Edison's way of keeping track of each series, but I have no idea why. The only change I know of in diamond stylus is explained below and I will be happy to e-mail a photo to anyone that is interested in seeing how this was done.
According to Edison Diamond Disc Re-Creations records & artists 1910-1929 page 107:
In this process the diamonds were first silver plated, then mounted on rods with paraffin, plated for 72 hours with nickel layers electro deposited under tension. The styli were thus held under layers of nickel at thousands of pounds of pressure. The nickel-encased diamonds were then polished to conical shape, the nickel at the stylus point being found away as the diamond was polished. The finished stylus was then soldered into its stylus bar. In the early days, bare diamonds were just soldered into bars and were prone to breakage when carelessly lowered onto the record.
The original DD styli were soldered in. The earliest bars have the bare diamond soldered in; the later ones were first plated with nickel and then soldered in. To understand this think of a wooden pencil the diamond is the lead. When the pencil is sharpened the wood is removed and the lead is shaped, the wood is the nickel and the lead is the diamond.
Yes, yours is one the other was on eBay, I suspect Edison converted some of the unsold tops he had as he never wasted. You have a very special reproducer and I am very fortunate to have a photo of it identified by its serial number. What makes Edison so much fun is all the varieties and nice people like you who share their good fortune. For about two years I was curious about the eBay one.