Working for a manufacturer of many products including epoxy materials - shelf life statements are not there to promote more sales. All major manufacturers exhaustively test product to ASTM standards of which there are many. And epoxy chemistry does change it's strength characteristics over a period of time. If anyone would like to see how epoxies change over time, I am pretty certain I can provide public data that illustrates this.
Shelf life statements are usually pretty specific as to length of time and storage conditions. In my experience, epoxies go anywhere from 2 months in a freezer to 2 years at room temp and everything in between. Products are warranted to be good during this period of time if the storage requirements are met. Outside of this period of time, no more product is warranted and the user of the material should toss it.
As far as the "technicians or technical support" reading off of a written document - they have to do this. They should not be providing answers to questions that they do not have the data to back them up. If they are saying make a small batch and see if it cures and if it does it is good to go - no way would I trust this answer. While it may look cured, there can be many things inside that "cure" that have changed over a number of years.
Personally, I would much prefer to purchase a product from a manufacture who sticks to the expiration dates and whose technical support people read from well written and documented data sheets rather than providing answers on the fly. Next time a technical support person provides an answer that is outside of what the manufacturer reports being good, be sure to ask them for the actual data that will support that claim. I bet the answer changes.
These types of materials are used to make everything from submarines to spacecraft. Can you imagine the liability to the company whose technical support staff went outside of known data and said "sure - if the product cures it is still good to go" and then something catastrophic happens that costs people their lives and the fault of the problem is traced back to bad resin. I wouldn't want to be that employee nor the manufacturer of the resin material.
One person's opinion.
Mark