I knew of the Plautus example (the earliest attestation of the quod indirect speech construction, I think) but not of the Pliny one. Interesting. I don't know how common the reflexive-for-passive construction actually is in medieval Latin. I don't remember ever coming across it, but then I guess this is the kind of thing that might be found in some regions and/or authors and not others, so maybe it's found in what I haven't read. Of course, it would have been a common construction at some point in late vulgar Latin/early Romance, leading to the construction found in modern Romance languages like French.