SB569 - when did the 12 year crank life limit start?

The first entry in the engine logbook is not related to the aircraft CofA.

The aircraft logbook is irrelevant.

That very first entry should be the date of installation of the engine i.e. the date it is mounted on the mounting frame and everything connected up. That happens before (possibly months or more before) the aircraft gets a CofA, because the CofA is done only on the registry of the country of the first customer.

Like hopefully all TB owners I have the original ex-Socata French-language logbooks (which probably very few pilots continued to write into and instead started their own fresh ones) and these show the engine installation date. They are fairly unlikely to show the CofA date unless the aircraft was sold directly by Socata to the end user, which was rare. Also, the majority of TB aircraft were issued with multiple CofAs, due to registry transfers, often weeks or months after the original delivery. If you have too much time on your hands, you can browse some TB regs here Don't ask me how that "spotter" compiled the data; it is amazingly complete (up to about 2008) and some of the stuff in there must have been obtained from a contact inside Socata, IMHO.

I saw the posting about the aircraft CofA issue but I believe there is no basis at all for that interpretation - especially as the Lycoming's customer service rep (who has been answering the same question all day long, apparently) specifically disagrees with it.

However, if your local CAA says XYZ is true, and you get that in writing, they cannot possibly prosecute you. A barrister told me once that under UK law they could prosecute somebody else (i.e. their incorrect information does not modify the law) but they cannot prosecute you because you are entitled to expect that kind of communication to be correct. In the UK, this principle has been tested many times, to the consternation of the CAA where they took somebody to court and in the court it was discovered that some low level CAA employee wrote letters to the defendant which he/she was not authorised to write

My view, which is obviously worth what you are paying for it is that while you cannot get prosecuted for flying an unairworthy aircraft, you might have hassles with insurance (the insurer is entitled to check the regs directly and is not bound by the opinion of some CAA employee) and in some other scenarios there might be problems with warranties (reason as before).

Personally, if I was in the "SB569 / AD [whatever number it is] not complied with" group I would attend to it with some urgency, because the Lyco crankshaft debacle affected something of the order of 5000 engines, the majority of the owners will not have been tracking this crazy situation by reading pilot forums on a regular basis over the past decade, and it's going to hit them hard pretty soon when their next Annual comes up and suddenly a few load of IAs in the USA will advise their client of this nice little $50k AD which needs to be complied with... The vast majority of aircraft owners take little or no interest in their maintenance, anyway, and in Europe the impenetrability of the EASA Part M system discourages doing so (while making the owner responsible for it legally!). At best there is likely to be a shortage of engines.

I also think that if the confusion over dates gets resolved to the more strict (and IMHO probably correct) interpretation, there will be a big stink because many planes will turn out to have been flying without a CofA for anything up to a year or maybe longer.