who signs last will be held responsible for the aircraft's airworthiness as a whole regardless of what has been done before
Do you have a reference for that? It is very much against natural justice and would never stand up in Court.
Take two scenarios I can think of, where I turn up at your firm for an Annual. Current TT is 800hrs; last Annual was done (different company) at 650hrs.
(1) My mags are at 800hrs, OH reqd at 500hrs, logbook entry exists to say it was done at 500hrs
(2) My mags are at 800hrs, OH reqd at 500hrs, no logbook entries on the subject
IMHO, in case (1) you are in the clear because
you are 100% entitled to assume that the logbook entry is not a forgery. Otherwise, please provide a reference to the contrary, and actual case law. This cannot be legal because it would make you liable for the previous firm's document forgery.
In case (2), it is not so clear, is it? I'd like to see the legal guidance on this, if there is any. You are entitled to assume that last company did the job right, no? If not, that opens a huge can of worms because basically every plane going for an Annual with incomplete past records will need a full Export CofA. But I can see a directive to this effect standing up legally - despite being practically unworkable because of how much detail do you go into? This would be dealt with with professional liability insurance; accountants and solicitors have the same problem (conveyancing is one example where you can be sued for previous peoples' stuff).
I have had situation (2) on my plane (more accurately, some logbook entry did not make sense because it showed some work was done but the # of hours was not related to any actual SB or whatever) and I had it re-done immediately. But hey this is my own plane, I know where it's been, and I maintain it with money no object (especially the single shaft mags
).