Glad you could identify the numbers.
Your second photo labeled "Inspect B" is the best example for me to guide you as to look for the other serial number. Looking at this photo, there should also be a matching serial number 2928 along the top edge of the steering head plate that is part of the backbone. The serial number is located directly above the slotted cross bolt that holds the front seat spring wire. Look for your 2928 serial number that you found under the front fork also stamped into the top edge of this plate. If pitted or surface rusted, take a small wire brush and scrub this edge of the plate to reveal the matching number. Revealing this number is not looked upon as ruining the originality but rather your diligent researching and identifying the bicycle. You "may" need to use a magnifying glass or a eye loupe if pitting from rust is deep. A bright flashlight also helps bring out faint stampings when looked at from different angles and getting reflections of the surrounding metal
Your serial numbers should match establishing that both front forks and back bone frame were dedicated parts for this bike when going through it's initial production in 1888 or 1889. Mismatched serial numbers mean many things: a back bone or steering head having another serial number was used as a replacement for a repair back in the day resulting from a crash, bent frame, etc. or if the complete front end (front fork, wheel, handlebars, pedals, etc) of the bicycle was found and a backbone was later added to build the bicycle back to original. The fact of finding the same size frame, year, make, model, etc seems nearly impossible and doesn't seem likely to be the case with your bicycle. I don't want to sound to way out there but in this research you have to rule out all the possibilities from my years of doing this as strange things happen in the world of collecting which I again, don't feel is the case here.
By finding these two matching serial numbers, you can ask on this site and someone (Dave Toppin or Carey Williams) has an ongoing list continually contributed to by modern day owners of other sister machines with their serial numbers to pinpoint if your bicycle is an 1888 or 1889 model. If your seat has the metal "pommel hook" that hooks onto the front wire seat spring or there are holes in your leather saddle that show a pommel was there if it is missing now, this was something that was on 1890 models so yours, to confuse things even further, still could be an 1888 or 1889 model fitted with this improvement of a pommel hook used on 1890-1892 models that used the 4th Kirkpatrick model saddle. Yours may be a cross-over machine meaning having a saddle from later year than what was advertised as that years saddle. Also the fact that the saddle could have been recovered later with the later used pommel hook is also a possibility.
Also have you looked to see if there is a metal plate between the leather wrap where the rivets are that hold the leather that is wraps back on itself at the front of the seat? This will be good to know since your bicycle looks like the leather seat is original and, as I had previously mentioned, this is the only thing that differentiates the 1888 and 1889 model as Dave Toppin and I found out some years ago by comparing two original bicycles. Also this way you can see from the list that people have contributed to if yours is an early or late model produced bicycle of the respective year by serial number for sure and then the fine tuning via how the seat is riveted with or without the metal plate at the front of the leather. Ultimately the serial number will be your most important reference as to where your bicycle places on the contributed list as the seat leather "could" have been changed out but the metal stamped serial numbers are the proof in the pudding.
Be patient as Wheelmen who are reading this will help you in a more educated way than you can imagine. You are now doing what most collectors do in finding what model and year bicycle you own. Only in this club will you be correctly guided by what I refer to as "fellow experts" in the field of antique bicycles of whom I know and have also known their fathers who passed this knowledge along to them to carry it on today. You are in good hands here.
Your bicycle, having the even surface rust patina all over it from many years, looks like it has been together since day one which is my observation.
From what I see from your photos your bicycle looks like an undisturbed bicycle and you will probably find the matching serial number where I have mentioned.
This research is fascinating to me and a lot of club members and is rewarding to find out exactly what you have and getting the satisfaction of doing something historic by your research of identification of your bicycle for future generations to learn from and refer to.
Happy sleuthing Dr. Watson, I mean Dr. Brian!
Mike Cates, CA.
