Hi Syed,
I think you've confused access sequence with condition exclusion
firstly, I don't think condition exclusion applies to text determination, it is for pricing determination only.
Secondly, you mentioned inside access sequence 99 you have two valid accesses, namely 0002 and 0003. Here you need to understand, whenever access sequence find a valid record, it stops searching next access. so if it finds a valid record 0002, it stops searching for 0003.
If you want both to apply to your header, here is the correct way to config it
maintain two text ID for header
for each text ID, maintain a separate access sequence.
in your senario, you would have text ID z001 and Y001 to your sales header
you would have access sequence 98 with text id z001 from knvv in it
you would have access sequence 99 with y001 from knvv in it.
check this link for step by step guide
http://www.learnsaptips.com/2010/09/text-type-configuration-in-sap.html