Method to extract certain Text patterns from a column, between the space and comma

I've managed to safely extract the part of the string between the comma and the last space before it using a combination of stuff, charindex, reverse, len and cross apply.
I write "safely" because a stuff based solution will not raise errors if it tries to parse an ill-formatted string, unlike substring based solutions that will, as you've seen, throw an "Invalid length parameter passed to the LEFT or SUBSTRING function" error.

First, create and populate sample data (Please save us this step in your future questions):

DECLARE @T AS TABLE (
    Col varchar(50)
);

INSERT INTO @T (Col) VALUES
-- Valid examples
('Smith Pa, Coleman'),
('John Pa-C, Fred'),
('Justin DO, Jack'),
('John OT, Press'),
('Jack ARNP, Nate'),
('Johm DPM, King'),
-- Invalid examples
('NoSpaceTITLE, LastName'),
('No Comma TITLE LastName'),
-- Strange, but not really invalid example
('Van Damme ACTOR, Jean-Claude');

Note: I've added to the sample data some invalid examples and and also an example that isn't really invalid but is different than other examples.

The query:

SELECT    Col
        , NULLIF(STUFF(BeforeComma, 1, LEN(BeforeComma) - CHARINDEX(' ', REVERSE(BeforeComma)) + 1, ''), '') As SafeTitle
FROM @T
CROSS APPLY (SELECT STUFF(Col, CHARINDEX(',', Col), LEN(Col), '') As BeforeComma) As A

Note: using cross apply allowed me to calculate the string before the comma once, but use it three times in the query itself.

Results:

Col                             SafeTitle
Smith Pa, Coleman               Pa
John Pa-C, Fred                 Pa-C
Justin DO, Jack                 DO
John OT, Press                  OT
Jack ARNP, Nate                 ARNP
Johm DPM, King                  DPM
NoSpaceTITLE, LastName          NULL
No Comma TITLE LastName         NULL
Van Damme ACTOR, Jean-Claude    ACTOR

See a live demo on rextester