I think that some of the Albergs will still be sailing in 40 years. A lot of them will not. There are two primary determinants that afffect the longevity of the fibreglass - mechanical force and chemical degradation.
The glass in the boats is actually pretty weak stuff, but when it is encased in the plastic resin, it becomes quite stiff. Once bent though, the crystalline structure of the glass is compromised and the perfect little cells become misshapen and weakened. They are not elastic in the sense that rubbers and some plastics are, so when damage occurs - it is permanent. This happens on a microscopic level every time the boat flexes as it sails through waves, and on a larger scale when the boat is subjected to trauma, such as running aground or banging into docks. Eventually, if all of the glass fibres become damaged, the boat will become so brittle that (in theory) any traumatic event will be enough to make it shatter, as the resin by itself has little structural integrity.
The second factor - chemical degradation, most familiar to boaters as osmosis, happens because polyester resin (all resins actually, including epoxy) are not really "waterproof". They dissolve in water.
The gel-coats used in the sixties and seventies were particularly prone to dissolving like this, with the result that they became porous enough for water to enter. The water then encountered the secondary layer of resin, less solvent than the gel-coat, hence it could not penetrate as quickly, so it accumulated and formed "blisters".
When a blister is "popped" close attention is paid to the colour of the liquid that comes out, as the darker it is, the more styrene is suspended in it, and the worse the degradation of the structure is.
The boats that are being built today, sometimes use materials that are less soluble than the resins used forty years ago, but they tend to use less quantities of both glass and resin, hence while it may take longer for them to start to break down, when they do start, they go more quickly, as there is simply less material to be destroyed.
So - to answer your question, the Albergs, being built with (by today's standards) an excess of both glass and resin, can handle a lot of banging around and sitting in water before they fall apart. If you find one that has been barrier-coated with epoxy, which, while still soluble is much more stable than polyester resin, and where bilges have been kept fairly dry, and that has not been rammed into the dock or run up on the rocks, then it's probably going to last quite a while longer.
If you are looking at one that has not been taken care of well, and has been banged around a lot, I wouldn't expect an awful lot from it. It would be quite difficult to determine exactly how badly a bot has deteriorated, but I think it would be safe to say that if you notice a lot of flexing when it sails, and if things start going out of alignment in the cabin (but don't confuse this with the normal swelling and contracting of wood), then the boat is on its last legs.
Probably a bit longer than you wanted to read but - WTH - I am feeling pedantic in the wee hours...