This explains part of my rotten old day yesterday,
just about every stamp I catalogued had a problem.
including then, this Seebeck without the wheel,
try finding this in Gibbons simplified
http://cjoint.com/data/ibd3SOoQBS.htm

Then I had a few from Venezuela that had no showing in Gibbons either.

Thanks for a very interesting story.

| The Scott Classic Specialized Catalogue
| of Stamps and Covers 1840-1940 notes that
| the last Seebeck issue for El Salvador
| in 1899, Scott 199-209, were not placed
| in use. The catalog values them only in
| unused condition. Stamps from this issue
| were later locally validated with a wheel
| overprint, issued and used. In addition
| to postage stamps, Seebeck and Hamilton
| also produced Salvadoran postal stationery,
| including 100 envelopes, 32 wrappers and
| 39 postal cards.