From their website:

"...Most of our yellow and white glues, including Titebond Original and
Titebond II, remain usable beyond two years. Should Titebond Original
become thick and stringy, or Titebond II turns into an orange colored
gel, these changes signify that the glue is no longer usable. The
minimum shelf life of Titebond III is stated as one year, when stored
appropriately at room temperature. Titebond III is expected to last
beyond its stated shelf life. If thickened, shake vigorously by firmly
tapping bottle on a hard surface until product is restored to original
form...."

"...we view the stated shelf life of most of our glues merely as a
guideline to avoid potential aging concerns. In reality, as long as
products like Titebond Original, Titebond II and Titebond III remain
fluid, without drastic change in appearance, they will continue to
perform as intended..."