As for your other finding, that HBS reports "success" if an incremental, let's call it B INC, to an incremental, let's call it A INC (or an INC to a FULL or DIFF for that matter,) even if a prior backup in the chain is missing is definitely concerning. While technically the backup is a success based on A INC and B INC only, as an end user I want to know that B INC was not only successful, but is RESTORABLE. I want the software to verify that every file in the chain is present so a RESTORE is likely to be successful. If speed is an issue with type of a check, at least give the end user the option to have the software check the chain, with a warning present if the option to NOT check is utilized. Now that said, I haven't tested the "verify" feature to see if does indeed check the full chain.
EDIT:
added info about the option to check the chain
EDIT:
added info about the option to check the chain