Get collection of the current voucher which is accepted

Code:

[Collection:colltype]

Type:        Vouchers:Vouchertype
Child Of:    $$VchTypeSalesOrder
Belongs To:    Yes

[Collection:collinvent]  
   
Source Collection:    colltype
Walk:                Inventory Entries
Compute:            stkdue:$$String:$Orderduedate


[System: Formula]

stkqtylist : $$fulllist:collinvent:$stkdue

hello

the above code gives the value of all due dates passed in all sale orders generated (comma separated).

I just want the due date of the sale order which is actually generated now. How to get the due date of the latest sale order which is generated?

Thank you!