Depends
Liquid,
DNP has an ideal shelf life of 3 months with an effective life of around 6 months once it has been capped. Although there won't be any harmful side effects from going ahead and taking it, you will probably notice about a 5% decrease in effects per month beyond 6 months. Therefore, based on you saying you have had this for 12 months, I would guess it is probably at about 70% of it's effective dose. Therefore, a 200mg cap would most likely give the same effects as a 140mg fresh cap.
However, please take this only as a "maybe". Depending on how much lite, air, moisture, etc. it has been exposed to, it may either have preserved better or it could be a little weaker. I would stick with taking the normal amount of tabs you have in the past, and just watch the way you feel. If you are an experienced user you should be able to note the difference between 280mg and 400mg.
Hope this helps......
Kemo