EFO
- Abnormalities/Freaks
- Airmails
- Alaska
- Birds
- Blind Perfs - Looks Imperforated
- Blocks
- Booklet Panes
- Christmas Seals
- Christmas Stamps
- Coils
- Collections
- Color Errors
- Color Proofs
- Color Shifts
- Computer Vended Postage
- Counterfeits
- Double Paper
- Double Printing
- Double Transfer
- Dry Printing
- Duck Stamps
- Envelopes
- Famous Americans
- Famous Buildings
- Famous People
- Flowers
- Full Gutters
- Full Sheets
- Holiday Stamps
- Imperforates
- Line Pairs or Strips
- Local Stamps
- Mail Early Blocks
- Mail Early in the Day
- Major Errors
- Miscut
- Misperfs
- Monuments
- Offset on Gum
- Olympics
- Over-inking & Under-inking Smears Blobs
- Pairs
- Plate Blocks
- Plate # Singles
- Postage Due
- Postal Cards
- Postal Service Blocks
- Precancels
- Pre-printing Paper Folds
- Presidents
- Reverse Printing Errors
- Souvenir Sheets
- Space
- Special Delivery
- Stamp Strips
- Tagging Errors
- Test Stamps
- Trial Color Proofs
- Untagged Errors
- U.S. Regular Issues
- U.S. Revenue Stamps
- Varieties
- Zip Blocks
- Zip Single, Pair, Strips
US Regular Issues
- Air Letter Sheets (UC)
- Air Post Stamps – Airmails (C)
- Blocks
- Booklet panes, booklets (BK)
- Carriers & Locals Stamps (LO, LB)
- Christmas Seals (WX)
- Coil Stamps
- Collections
- Cut Squares/Envelopes & Wrappers (U, W)
- First Day Covers
- Mail Early Blocks
- Plate # Singles
- Plate Blocks
- Postal Counterfeits
- Precancels
- Souvenir Sheets
- Special Delivery (E)
- Test Stamps
- United Nations
- Zip Blocks
- Postal Cards (UXC)
U.S. Revenues General (R)
- Cigarette Tubes (RH)
- Consular Service Fee (RK)
- Documentary (R)
- Duck Stamps (RW)
- Future Delivery (RC)
- Narcotic Tax Stamps (RJA)
- Newspaper & periodical Stamps (PR)
- Official Stamps (O)
- Offices in China (K)
- Parcel Post Postage Due Stamps (JQ)
- Parcel Post Stamps (Q)
- Playing Cards (RF)
- Post Office Seals (OXF, OXA, OX, LOX)
- Postage Due (J)
- Postal Savings (PS)
- Potato Tax (RI)
- Proprietary Stamps (RB)
- Silver Tax Stamps (RG)
- Special Handling
- Stock Transfer (RD)
- Tobacco Stamps (RJ)
- War Savings Stamps (WS)
- Wine Stamps (RE)
