Sorry, but the more I think about this, the more I'm convinced there would NO, NADA, ZILCH, ZERO deterioration of the rubber hose in storage. It should be as good today as the day it was purchased.

First off, no one uses real rubber tree sap for anything anymore. Almost all of the BLACK "rubber" we come across in our lives nowadays (but I'm not sure about car tires) is made of either neoprene or nitrile "rubber", both of which are synthetic rubbers ultimately made from crude oil. I've heard of polyurethane garden hoses, tho, but they're made in various colours, not just black.

Now, here's the kicker...

I still have nitrile rubber beveled washers in a paper bag that my father purchased over 50 years ago for repairs in a commercial building he built in Selkirk, Manitoba back in 1960. I hung on to those washers thinking I might need them for something, but never did. Now, these things are over 60 years old, but they're not rotting, they haven't turned hard, and exposure to the oxygen in the air has had no perceptible effect on them. Except for their shape, they still appear in every respect to be exactly the same as a brand new rubber washer would be. If those old washers have lost any of their elasticity, it's lost on me because they still appear to be perfectly usable.

Virtually all the rubber used in plumbing is nitrile rubber (formerly called "Buna-N" rubber). It is well recognized that EPDM rubber is actually more resistant to water than Nitrile rubber, and brand new faucets might come from the manufacturer with EPDM O-rings in them. However, since O-ring manufacturers don't know what their O-rings will be used for, and Nitrile rubber has excellent resistance to BOTH water and hydrocarbons like oils and greases, far more O-rings are made from nitrile rubber than any other synthetic rubber. Nitrile O-rings are produced by the millions and sold in every hardware store in the world, whereas you have to go to a place that specializes in pneumatic and hydraulic seals to buy an O-ring made of anything OTHER THAN nitrile rubber.

So, if there's a "rubber" liner inside those braided stainless steel washer supply hoses, it's either a nitrile rubber liner or an EPDM rubber liner. And, as stated before, I have old nitrile rubber beveled washers that haven't deteriorated to any perceptible extent as a result of 60 years exposure to air, and I expect this forum is full of guys that have old nitrile rubber plumbing parts they bought decades ago but never used that can confirm there's been no perceptible deterioration of that stuff either.

So, instead of saying that "I'm uncomfortable agreeing with the premise that the rubber would deteriorate.", I'm going to restate my position as "The rubber doesn't deteriorate to any perceptible extent during a normal human lifetime."