So, you can track for many hours without drift.
Last night I imaged The Jellyfish for 5 hours straight.
Isn't 5 hours a long time to expect the mount to track perfectly? Even if you drift align you are ensuring no star trails for only 5-20 minutes or so. Michael Covington in "Astrophotograpy for the Amateur" explains that a misalignment can result in an fast/slow tracking rate and/or field rotation depending on the direction of the misalignment. However guiding should have corrected the fast/slow tracking rate problem.