Hi Adhikesh,
I guess i can help you with this issue, recently we have deployed PCo. So, to answer your question consider below scenerios
1. Which agent you are using, if you are using DA agent then it will only give the recently updated values .ie. the current values of the tags irrespective of time. For example you queried for Tag T1 and Tag T2 for same start and End time Which is ST, ET but Tag T1 got updated most recently at time ST1 and T2 at time ST2. Now in the output you will see ST1 and ST2 time not the time given by you which is ST and ET. For multiple/Single row you can check/uncheck the Get Response in Multiple Rowsets check
2. If you are using HDA agent and want to get the most recent values then you can select mode as Aggregate list and in Tag Aggregate Query you can select group as "END" to get the latest values.
Permutation and Combination of above two will give you all the possible solutions needs .
Hope it is useful for you, please let me know if you need more details.