Beer is basically an agricultural product. It uses hops, grains, yeasts and water. If any of those things change then the beer changes.
Example: Sitting at Kuni's Sushi Bar a number of years ago enjoying our usual Asahi 'SuperDry'. Tastes slightly different. Look at the label, Imported from Canada!
Only place I can get Superdry from Japan is now in 1 liter cans at Mitsuwa and who knows for how long.
Example: Miller purchases rights to Lowenbrau name and has beer made in Canada, tastes nothing like original beer, brand becomes extinct in US. Current revival tastes nothing like original.
So, methods of production of the ingrediants change over time as do the sources of where they are grown. The result is, none of the beers of 30-40 years ago taste the same today. Schlitz went to a cost saving, faster brewing process and lost thier market. Nothing can bring back Schlitz as well as the 100's of small brewers that existed in almost every Wisconsin city in the 1960's.
The most constant source i know of has been some of the German producers notably Hofbrau and a few others that manage to maintain a style and make real beer. there are some good craft brewers in the US and I have sampled a lot at Brew Fests. These are much better than any re-introducution of an old 'Formula'.-Dick