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The yellow BPNs are EXTREMELY difficult to read with the naked eye. They are slightly legible under decent magnification, but generally it is easiest to read the yellow BPNs by photocopying the note, or scanning it into your computer and manipulating the colours in Photoshop.
Blue BPNs are normal beginning with EOH 2600000. They are not replacement notes. Replacement notes in this series were ENX, FNX, ANX, and the GOT, GOV, GPH, ANH, GPZ and HNA insert ranges.
The EPW good-overs are all known to have blue BPNs, not yellow. If you were to find an EPW note (or any note after EOH2600000) with a yellow BPN, this would constitute a previously-unknown variety and should be reported in detail here on the forums.
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BWJM, F.O.N.A.
Life Member of CPMS, RCNA, ONA, ANA, IBNS, WCS.
President, IBNS Ontario Chapter.
Treasurer, Waterloo Coin Society.
Show Chair, Cambridge Coin Show.
Fellow of the Ontario Numismatic Association.