Hi :
You have experienced warehouse crystallization . Most times the plastic will discolor giving you a hint .Other times it will be more brittle when handled , Such as cutting it off the sprue .Then there's the worst , which you cannot figure on .Plastic is processed using heat .Sometimes the heat drifts to high in the machines and the resulting product becomes brittle later .
Then it's stored in many warehouses before it gets to you . Who knows what the condition in the warehouse was . I feel for your loss as I completed a sailing ship ( AIRFIX'S - H.M.S. VICTORY ) ( the large one ) And my feline friend( Long Gone ) thought the ship was a new toy for him , on the mantle . I was finding shards , Yes , shards , months later ! No , the cat in this message lived to the ripe old age of fifteen and died in his sleep .