The 'common' ones do. It's harder to test the 'uncommon' or 'rare' ones due to the type of bonuses they provide. I tried testing two stacked rotation bulletins for the stug 3 and it seemed to work, but without seeing the default rotation speed it's hard to be 100% sure.
If anyone has two or more of any 'uncommon' or 'rare' bulletins that effect the cost of an ability then please stack them and test to see if the price is effected multiple times or only once.
So this all basically means that Relic need to change their official statement to something like "Duplicate 'common' bulletins do stack, but 'uncommon' and 'rare' ones [insert if they stack or not here]. Sorry for all the confusion. We do know what we're doing...honest!"
"The one thing they did do right, and all credit to them, is the Free Commanders"