This is especially problematic, as retrofitting correlation IDs in is very difficult; you need to handle them in a standardized way to be able to easily reconsititute call chains. Although it might seem like additional work up front, I would strongly suggest you consider putting them in as soon as you can, especially if your system will make use of event-driven architecture patterns, which can lead to some odd emergent behavior.
Add correlation I'd tracking as early as possible. Now.
