Substring Questioin

declare @bid table(
streetNumber varchar(10),
streetName varchar(100),
streetNameSuffix varchar(100)
)

insert into @bid (streetName)
select '12 union street' union all
select '1A apple avenue' union all
select '11A apple st avenue road' union all
select 'POB 23'

select * from @bid

update @bid
set streetNumber = case
when substring(streetName,1,charindex(' ',streetName)) like '[1-9]' OR
substring(streetName,1,charindex(' ',streetName)) like '[1-9][1-9]' OR
substring(streetName,1,charindex(' ',streetName)) like '[1-9][1-9][1-9]'
then substring(streetName,1,charindex(' ',streetName))
else null
end,

streetNameSuffix = case
when substring(streetName,1,charindex(' ',streetName)) like '[1-9][a-z]' OR
substring(streetName,1,charindex(' ',streetName)) like '[1-9][1-9][a-z]' OR
substring(streetName,1,charindex(' ',streetName)) like '[1-9][1-9][1-9][a-z]'
then substring(streetName, 1, charindex(' ', streetName))
else null
end,

--streetName = substring(streetName, charindex(' ',streetName) + 1, len(streetName)-charindex(' ',reverse(streetName))-charindex(' ', streetName)) + ' ' +
--substring(streetName,len(streetName)-charindex(' ',reverse(streetName))+2,len(streetName))

streetName = substring(streetName, charindex(' ', streetName)+1, len(streetName)-len(charindex(' ', streetName)))

select * from @bid


how can i write my code in order for the "POB 23" to stay the in streetName field?