Having a question ref spare oil storage

[pavproch]

For at least 15 years I kept to the following: Every 2 or 3 years purchasing 20 (25) liter drum of spare oil for my Zet (MillersOils CFS 5w40 NT+) and used it upon my needs = ie. storing half empty/half full drum for a year or two (always lidded, of course, at room temperatures in darkness) until I run off it and purchasing a new drum. But quite recently I got a "disgusting" comment on that - "I would NEVER use oil stored like this" but with no further (technical) comments or explanations.
Over the years I never came across any issues related to degradation (oxidation? or else?) of my oil stored like this.
Consequently, I found somewhere something about the issue:

An opened bottle of fully synthetic should be good for 5 years from opening, as long as you’ve kept it sealed when not using it.

Whilst (at the other forum) receiving a baffling reply (attached).
In my case the opened drum never lasts longer than approx 2years.... and no issues whatsoever.
This is simply / rather confusing.....

Is there anyone (= a real expert in tribotechnics/lubrications) to comment some pros and/or cons to such a way of storing spare oil?

 

[Christopher72]

I change my oil in the fall and the spring, even though it's never driven in the winter. Keeps the engine fresh and the additives doing their job. To be honest, it's cheap upkeep, especially since I return the used oil under its lifetime warranty for credit.

I'm sure your stored oil will work fine, just not ideal. Perhaps the tradeoff is to change it on a more active schedule.