From this video I learned that the first two digits of the original MITS Altair 8800 were always 22. Interesting.
I discovered that right behind me in my workshop I have had the 43rd MITS Altair kit made. Serial number 220043K. Wow. This kit would have been shipped in January 1975. At the time there was a huge demand for the kits and I don't think it's unreasonable to assume they shipped at least 43 kits by the end of January. That also assumes the kits were mailed in the same order as the serial number, but I don't know.
Bruce had factory-assembled #47, a boxed Altair 8800 with S/N 220047A - where the "A" indicates factory-assembled.