I would not hesitate to use a Milepost or Church book that was several years old. Newer ones will be more up to date of course.
In 2013 I emailed the Church's that 2 of the 3 CGs in Watson Lake were closed. Their delayed response was that they had seen that earlier in the year. No big deal but by the end of the summer it still was not in their online updates so I'm not sure why they even have a online update. The book is very good but like anything not always accurate. It's all part of the adventure and one should expect the unexpected.