There were two different 1 cent Omnibus stamps. The original stamps, if you have a long strip, will show a plate number every 24 stamps. Since your 1 cent is a coil of 30, you must have Scott 2225. It is recognisable by the larger 1 and the lack of a c for cent.
These stamps were printed on thye B or the C/D press, and here the platenumbers are 52 or 48 stamps apart!
Scott lists three different stamps, depending on the type of tagging.
If you'd like more info on these coils, go to
www.pnc3.us/pnc3.org for much more info.
Peter