Let's say that you're thinking of applying for TT jobs in the U.S., though it's not absolutely essential for you to do so this year (but there are some opportunities you don't want to pass up). Due to some peculiar circumstances, there's no one who can really write a letter commenting on your teaching abilities based on observation in the last 5 years. I mean, yes, you did teach a few classes in that time, but you didn't have the presence of mind to ask someone to come observe them. Let's say, to make things really interesting, that you're not teaching right now, so you can't have one of your colleagues just come observe one of your classes (and maybe you don't feel like announcing too prominently to them that you're considering other jobs). There is, of course, the letter you got as a graduate student written by a professor you taught section for a long time ago.
What's the preferable course of action?
- only apply if you can somehow arrange things to get a new letter.
- don't worry about it and use the old letter.