SAS PROC FORMAT - Define 'Other' Range for Numeric Variable - format

Question

I've created a format that assigns a State label to a pre-defined range of Start-End numeric postcodes.
i.e.
Start | End | State
2600 | 2618 | ACT
2900 | 2949 | ACT
4000 | 4899 | QLD
I want to add a piece of code to the format file that assigns it a label "Error" when the postcode falls outside of my range.
In a previous thread, someone suggested using the HLO solution but I have tried implementing it with mixed success.
rsubmit;
data Fmt_State;
set State end=eof;
retain type 'n';
fmtname = 'category';
start = pcode_fr;
end = pcode_to;
label = State;
* For the first observation, assign the ‘LOW’ keyword;
if _n_ eq 1 then HLO='L';
if eof then do;
*** For the last observation, assign the ‘HIGH’ keyword and output;
HLO='H';
output;
*Define an 'Other' range that is outside the bounds of LOW and HIGH;
HLO='O';
label = "Error";
output;
end;
else output;
run;
endrsubmit;
Oddly, only the Middling ranges BETWEEN Low-High that are correctly labelled Error and the ranges outside Low-High that are incorrectly labelled. (I would expect the opposite to be true but still not working the way I want)
For clarity this is what's happening from my same ruleset:
Pcode | ShouldReturn (Reason) | ActuallyReturns
2615 | ACT | ACT
2000 | Error (TooLow) | ACT
2700 | Error (Undefined range) | Error
5000 | Error (Too High) | QLD
I just want anything undefined to be called Error despite it being too low or too high. Please help!

Answer 1

Your logic is incomplete. You want to add three new records.
START END HLO LABEL
. 2600 L Error (Too Low)
4899 . H Error (Too High)
- - O Error (Undefined range)
So you want logic like this:
if _n_=1 then do;
start=.;
end=from;
hlo='L';
label='Error (Too Low)';
output;
end;
start=from;
end=to;
label=state;
hlo=' ';
output;
if eof then do;
end=.;
start = to;
hlo='H';
label='Error (Too High)';
output;
hlo='O';
label='Error (Undefined Range)';
output;
end;