Depends on the given Club. If it's the VMCC (and VCC?) or an OC for a British-made vehicle, DVLA have to "take the Clubs dating officers word"; because, by virtue of the records that came out of the Science Museum to the VMCC (and VCC?), who then passed on relevant bits to OC, it's Clubs that have "the manufacturer/factory record" and it's usually the dating officer that has access to it. What's tightened up afaict is, whereas in the past a Club dating officer perhaps simply looked at "the manufacturer/factory record" for the details to put on the dating certificate, now DVLA want some sort of copy/"extract" of that "manufacturer/factory record".
Perhaps curiously, the "extract" isn't necessarily a photocopy of the manufacturer/factory record - probably because most were originally one hand-written line on a big ledger page and some are damn' hard to read. Just whatever's provided by a Club dating officer, the Club and the format must be acceptable to the DVLA. What's apparently different is you aren't allowed to call 'em "dating certificates" anymore ...
Otoh, if - perhaps because the Club is for an obscure foreign make - the dating officer can't supply any "extract from the manufacturer/factory record or an extract from the appropriate ‘Glasses Check Book’", then "the Clubs dating officers word" isn't acceptable on its own.