<Tr> <Td> Ohio </Td> <Td> State </Td> <Td> US - OH </Td> <Td> OH </Td> <Td> 39 </Td> <Td> OH </Td> <Td> OH </Td> <Td> Ohio </Td> <Td> Ohio </Td> <Td> O., Oh . </Td> </Tr> <Tr> <Td> Oklahoma </Td> <Td> State </Td> <Td> US - OK </Td> <Td> OK </Td> <Td> 40 </Td> <Td> OK </Td> <Td> OK </Td> <Td> Okla . </Td> <Td> Okla . </Td> <Td> Ok . </Td> </Tr> <Tr> <Td> Oregon </Td> <Td> State </Td> <Td> US - OR </Td> <Td> OR </Td> <Td> 41 </Td> <Td> OR </Td> <Td> OR </Td> <Td> Oreg . </Td> <Td> Ore . </Td> <Td> Or . </Td> </Tr> <Tr> <Td> Pennsylvania </Td> <Td> State (Commonwealth) </Td> <Td> US - PA </Td> <Td> PA </Td> <Td> 42 </Td> <Td> PA </Td> <Td> PA </Td> <Td> Pa . </Td> <Td> Pa . </Td> <Td> Penn., Penna . </Td> </Tr>

When did washington abbreviation change from wn to wa