The "decades" Walkers crisps all seem a bit arbitrary. As well as the lamb ones for the '60s (which are the worst of the bunch, as far as I can tell), there's:
1950s: Coronation Chicken
1960s: Roast Lamb & Mint
1970s: Cheese Fondue
1980s: Chicken Tikka Masala
1990s: BBQ Rib
2000s: Sweet Chilli
Cheese Fondue is probably the only one of those where I'd be able to have a guess at the "decade" from the flavour if I didn't already know them.
Coronation Chicken's a bit of a giveaway, surely?