To me, oxygen permeability in a triangle-marked “7” carboy is pointless
I would never use one for storage regardless of the length of time. Just a bad practice.
The chances of leaching BPA or other chemicals with estrogenic activity, or toxins or carcinogens is not worth the couple dollars saved. Further, anything other than PETE or glass ... for instance polycarbonate, polypropylene or polyethylene ... *are* specifically known to be much more permeable to oxygen than PETE.
I would only use carboys that are marked PETE “1”.
Plastic carboys of non-PETE composition I only use for storing things like dechlor’ed water that I am going to use.
For longest term storage, bottling is pretty much the most practical way to do it. That said ...
For storage of up to 2 years, the safest bet is actually with a Better Bottle or a fairly new glass carboy that has not been banged around or gone thru freeze/thaw cycles (microscopic cracks in glass carboys also allow in oxygen over time).
Regular, non-Better-Bottle carboys made of PETE I’d suggest are safe for bulk storage of about 10 months or so.
Could you possibly get away with storage for a much longer length of time - or in some other vessel? ... sure, you might just get 5 years storage in a goat's stomach and have the wine still drinkable.
The question is how big of a loss is it if your batch goes south. Anecdotal stories of someone's cousin's brother's uncle storing successfully for multiple years using nothing more than a jerry-can and a balloon don't mean that is a storage method which can be relied upon.
Part of oxygen permeability is from the composition material ... part from the structure as manufactured ... and part, significantly from the closure. Better Bottle actually uses a specific high pressure blowing/molding process that was designed to maximize carboys resistance to oxygen permeability that other PETE carboys (the ones from Absopure for example) do not.
Not to get too off on a tangent here, but, the closure/stopper is a bigger culprit than the carboy generally.
The common silicone or PVC stoppers are NOT suitable for long term storage and are notorious for allowing in oxygen long term.
The best against oxygen infiltration are PETE stoppers, the closure products from Better Bottles, and also natural rubber stoppers and carboy-caps. Although with natural rubber, very old ones will eventually dry out.
The old, stinky black or red neoprene stoppers are also decent against oxygen infiltration ... it just the odor potentially getting into your product that seems to be a downside.
No, I do not have any connection to Better Bottles whatsoever ... and yes, here is a link discussing their closure systems ...
BetterBottle (Better-Bottle) Fermentation Products – BetterBottle PET Carboys
As I do not bulk store wine for more than about 6 months or so, I use PETE carboys and glass carboys with just plain-old stoppers from the brewers/vintners supply.
If I bulk-stored longer, I’d be doing as I say above.
But I’m cheap ... er, frugal. And own a lot of bottles.
People want a one-stop-shopping, silver-bullet solution to things.
The real solution to avoiding spoilage - oxygen and otherwise - is largely all the things done during the production and handling before the wine gets sealed in the carboy or bottle.
A lot of things put together are what keeps wine during longer term storage.
In any regard, using a triangle-marked-7 carboy is a nonstarter for me. If ya don't use em, ya don't have to worry about oxygen permeability in them.
(Wow. Read all that. Better than Ambien?)