QUESTION:
Is it possible to use non ID form when passing value prompt answers like valuePromptAnswers={Month1@Sort_ID}?
STEPS TO VERIFY:
1. Create a new attribute month1 with a third form Sort_ID based on Year_ID

2. Create a report containing value prompt per KB15734 based on Month1@Sort_ID

3. Create a document with Month1@ID in detail section.

4. Edit links on Month1 text box to link to report in step2:
http://10.27.73.98/MicroStrategy/asp/Main.aspx?Server=10.27.73.98&Project=MicroStrategy+Tutorial&Port=0&evt=4001&src=Main.aspx.4001&reportViewMode=1&reportID=BD9247794972DA96D5443EAF0F15E934&valuePromptAnswers={Month1@Sort_ID}&uid=administrator&pwd=
5. Run document and click on any text like 201401

6. Target report will return all months in year 2014

CONCLUSION:
Non ID form can be passed as value prompt answers like valuePromptAnswers={Month1@Sort_ID}