Experience has taught us that, specially for Direct Mail projects, 
production needs to be involved from the very beginning of the process.
They need to work with Account Managers, be aware of strategic objectives, and with Creatives as well.The DM production specialist is trained in a completely different discipline than their print counterpart. 
It is their job to see that press schedules are met, that elements fold, fit, 
function according to multi-layered plan. 
When you deal with personalizations, multiple elements 
(OEs, letters, Buckslips, Response devices, Brochures, Premiums, etc.) 
requires a tremendous organization skills, 
attention to detail, and understanding of budgets and timelines.
Add to that the element of multiple versions, 
as many tests may be taking place consecutively, and you see a maze of complexity that only those with special training can understand.
This also applies to other channels -- TV, Web, Email -- where versioning is part and parcel of the communications scheme.
Lack of qualified production people has been a key reason in the failure of many DM projects we've see in Latino agencies.