This lines up with what Ross Coulthart pulled out of Burlison directly in that NewsNation Reality Check sit down. Burlison was blunt that even the SCIF briefings weren't fully transparent, and that the first wave of released files was, in his words, the low hanging fruit. The material he considers most significant hasn't been released yet.
Two specifics worth flagging for this discussion: he described unreleased orb footage as balls of plasma moving intelligently, which he sees as more compelling than most of what's public so far. And he's specifically going after contractor held files, naming MIT Lincoln Lab, MITRE, and RAND as places where UAP related material may be sitting outside normal FOIA channels.
On the secrecy question raised above, Burlison's read is that it's less about public panic and more about institutional embarrassment, agencies not wanting to admit they don't understand the phenomenon.
I wrote up the full interview with timestamps and background on Coulthart here if useful: https://uapdisclosurereads.com/eric-burlison-uap-scif-interview/