Pierce Piano Atlas, 8th Edition, 1982, (ISBN 0-911138-02-1) has the following (very limited) separate entries:
WESSELL, Charles A. - 222 East 30th St, NYC (no other info about him)
WESSELL, NICKEL, and GROSS - piano action - started 1874 (no more info)
WESSELL, S.M. - serial numbers listed for pianos built between 1900 - 1909 (lowest number 18000 to highest 28400)
It appears all these WESSELL folks may have been related. Perhaps Charles started things ca. 1870's on E. 30th St, then S.M. (son ? nephew? cousin ?) took over the business later on. Very likely this small company was taken over or voluntarily agreed to merge in/after 1909 with a larger manufacturer (maybe Steinway ?), who may have wanted the gain the patent to the action developed in 1874. This kind of thing happened in the "piano biz" all the time.
The Steinway folks on Long Island have very good records of their own pianos made in USA, going back to 1853 or so. If they did take over this company, they may have kept the Wessell family member[s] on staff to retain the acumulated history. If so, there may be more info for you from Steinway archives.
Do we know if "The Piano Maker" by Alfred Dolge is still in print and available somewhere ?