I'm not sure I understand the source of your continued confusion about VendTrans, VendTransOpen, and SpecTrans. Perhaps we should just go over the sequence of events from start to finish.
When you're working in a Vendor payment journal, you are creating LedgerJourTrans records, typically with account type Vendor and offset account type Bank, for example. If you merely do that and then post the journal, you will impact Vendor balance and Bank balance, creating VendTrans and BankAccountTrans records. You do not have to settle any invoices, it is not required, even though it is the typical workflow using a payment proposal.
When any VendTrans record is created that is not 0, a VendTransOpen record is created to track the outstanding amount not yet settled. Eventually when the VendTrans record becomes fully settled, the VendTransOpen record is deleted.
Now the next most complicated case is working in a Vendor payment journal, still creating a LedgerJournalTrans record for Vendor offset Bank, but now you're selecting invoices to settle, hence the SpecTrans records. SpecTrans records merely connect two different records together with an amount. They are not in themselves a settlement. Instead, they represent a future settlement in the same way your LedgerJournalTrans record represents a future VendTrans (and VendTransOpen) record. When you post this journal, a VendTrans, VendTransOpen, and BankAccountTrans record are all created. Then, in a subsequent step, the SpecTrans records are used to settle the new VendTrans record (the new payment) against other VendTrans records (invoices). If invoices are settled in full, then their VendTransOpen records are deleted. If the payment is settled in full, then its VendTransOpen record is deleted.
There is no requirement to fully settle payments or invoices when posting a journal. If you want to see for yourself, post a payment of $1,000 and settle an invoice of $500. This will leave an unsettled payment on the vendor account. There is nothing wrong with this, i.e. prepayment.
So in summary, VendTrans records always (when non zero) create VendTransOpen records when they are first created. Then settlement consumes part or all of these VendTransOpen records. When a VendTransOpen record is fully consumed, it is deleted. This can all happen within a single journal posting, so you might be left thinking that no VendTransOpen record ever existed, which is a false conclusion.
Hope this helps.
