How Do You Contract Based on Vague Answers?

Recently a vendor asked for a copy of a winning proposal.  I've learned this is normal for US vendors to do, but in Canada, not so much.  In our discussion they came to realize there are two main reasons for this: Canadian protection of privacy legislation, and the RFP is a contract!

1) FOIPPA/PIPA/PIPEDA - these are the overriding privacy law in various parts of Canada - FOIPPA in the province of BC being the one I'm most familiar with.  To release an RFP would require a Freedom of Information request; a timeframe for a response; and a great deal of time and effort on the part of an FOI officer to redact the information.
The flipside of this legislation is the proponent doesn't get to mark 'everything' as confidential and a proponent doesn't necessarily get notified if an FOI request has been made. Although many organizations do the courtesy of giving them a heads up, by law the information is to be released and the proponent cannot stop it.  The information would have to be proven to be proprietary and marked as such before submission....and no, marking the proposal as 'confidential & not to be released without permission' does NOT override the law.

2) RFP Contract - in the US, the RFP is an advertisement; in Canada, the RFP is an offer. In responding to the RFP, proponents accept the terms/conditions of the RFP and form a contract with the buying organization.  This means the buying organization has to play by the rules as set out in its document.  That means the buying organization must score/evaluate the proposal against the weightings & criteria contained in the RFP. What some US vendors don't realize is their proposal is the 'final offer'; what is contained in their written proposal forms their evaluation score.  There's no new information submitted 'later'.

In our vendor debriefing discussion, the US-based vendor admitted they keep their proposals 'vague' because of the number of times their proposals are released to their competition (in the US). As a result they scored much lower.  It causes me to wonder: How does a buying organization make a procurement decision on a vague proposal?  How does one evaluate if the response to the written criteria has no details?