VCs do not have to be transparent until they open up investment to the public. So we don't have access to the internals of just any non-publicly-listed company.
True, but I used to work at a VC, as well as consulting to several others, and was also in the management team of several VC- and angel-funded startups.
I have never encountered a VC hiding any investment they made(*). On the contrary, they're very prominently headlined, both by the VC so that its investors know it's actually investing the money it has and putting it to work, as well as by the recipient companies to gain respectability in the eyes of customers, employees, and additional investors -- none of them is likely to take a company seriously if it's not clear it has enough money to keep the lights on. There's simply no motivation to keep investments secret.
(*)The only exception is startups in full-stealth mode, but Lightning isn't.