For advertising, this was a decade of change. The creative team system was pioneered, talented kids from the gutter were hired to challenge the Oxbridge hegemony, and a completely new creative style emerged. Given that backdrop, might JWT have yearned for its lifelong partner to become a bit more adventurous? Was Unilever's head turned by the young, sexy hotshops, whose work had a twinkle in its eye?
Certainly, the 60s reel displays a telling polarity, as though the two partners were torn between the instinct to stick to their ways, and an impetuous compulsion to Do Something Different. It's the latter stuff that catches the eye today, but for the wrong reasons: as a kind of curiosity, like looking back at an old photo and saying: "Did I really used to wear that?"
The Sea-Witch spot, for example. This is a James Bond spoof involving a speedboat, seven men in black, various robed women sat like limpets on rocks, resembling the souvenirs you get on the Isle of Wight, and some truly appalling jazz. To be fair, the task of selling hair colourants in black and white would have taxed the best of us, but this is one that hasn't stood the test of time.
Another brand, another boat. Pond's finds two women on a cruise talking about skincare. The one who uses Pond's gets violently whisked away by a buccaneer. It entertains - as the new 60s style demanded - but it doesn't involve.
By contrast, the classical, heartland work on the reel fares well from today's perspective.
Persil asks, "What is a mum?" and answers, in a candidly cast commercial, with some wry observations on the realities of the mother-son relationship.
Lux doesn't muck about. It eschews irony, humour and subtlety (all coming into vogue in 60s advertising) in favour of scale. Here, Ursula Andress simply and stunningly invites us to share the secret of her perfect skin.
The Sunsilk launch might look tame by today's standards - girl on beach, sun in hair - but it's easy to overlook the fact that it's based on a deep thought: that "A girl's most important cosmetic is her shampoo." A real consumer insight from the days when nobody used the phrase "consumer insight".
Oxo most satisfyingly exemplifies the classical JWT-Unilever approach.
Over the years, it has looked at the British family with frankness and affection, exploring the role of food in the innate drama of the common domestic incident. In the 60s it was Katie (no Ursula Andress, but sexy in a wholesome kind of way) who showed us how to knock up bangers and mash on a rotten day, or welcome a kid back from first day of school with something called Hasty Pie.
It's the quality of empathy that unifies the best of this work. There is something, some nugget, some simple human truth, which draws you in across the decades, and connects despite the ponderous editing, the long, explanatory voice-overs, and the all-white cast with their 40-year-ago haircuts and implausibly decent accents.
You could - we do - work with the same core thoughts, the same core ideas, and update everything around them.
Enduring idea meets fresh execution. Could it be the recipe for a few more anniversaries yet?