I did not have any problems with TN I-129 PP. My last two employers used to file PP whether for an extension or for a new TN for a new employer. One thing though: my new employer checked the box for "replacement TN" so I couldn't work for both employers at the same time. You can have multiple TNs at the same time and I had done that at the border before. But some employers don't like that because of conflict of interest due to working for a competitor concurrently. So if they check that box, once the new TN replaces the old one, you won't be able to work for the old employer which results in not being able to give a 2 week notice.