So I think both of us likely do some work in gov contracting, but I'm admittedly mostly on the side of those items typically procured only under the UPA, so I'll disclaim too much familiarity with any of the other sections.
I think we're perhaps speaking past each other a little, so I'll clarify - I agree that it's typical and legal process to keep the bids and proposals themselves sealed, until either the bids are opened or awarded, as you mentioned. Since this is a 2 part procurement with an RFQ prequalification stage, I'd say that its expected that the RFP would typically only be provided to those prequalified bidders. even if it includes "learnings" from the RFQ stage and takes into account information from prospective bidders, anything in it will have been handed to all qualified bidders. and my understanding is that there's a defined Q&A period prior to submittal that is typically "face up" - I believe common practice is for everyone's to be shared with all bidders. Absolutely the actual proposals themselves, and once they're opened the evaluations leading into BAFOs and the negotiations themselves should be confidential until an award decision is made, and even after are occasionally published redacted of sections respondents would have had to specifically disclaim as proprierary/confidential. but what the Globe wanted here wasn't the proposals from the respondents - its the RFP that was issued by the MBTA.
See MGL Ch 4, § 7 c. 26(h) - proposals and bids, but it's notably silent on the RFP itself, which in other chapters like 30A is specifically called out to be publicly available. That RFP is effectively a statement of the T's requirements it wants a prospective operator to meet, and there really should be no confidential information in that document, since it's been provided to all qualified bidders, written by the public agency, and can't be revised after closing. In the single phase procurements I'm more used to, its just about the core public facing document posted for transparency's sake leading into a procurement. Even if you're not a qualified bidder, and any bid you make would be rejected, my experience is that anyone should be able to see the plans and specifications and end up on the plansholder list. (Some security exceptions apply).