1. Completeness: The value of the books will be higher if they are all present and in good condition. If any books are missing or have significant damage, it can affect the overall value of the set.
2. Condition: The condition of the books is an essential factor in determining their value. Books with torn pages, water damage, or other significant defects will have a lower value compared to books that are well-preserved.
3. Binding: The type of binding can also impact the value. Hardcovers are generally considered more valuable than softcovers.
4. Market Demand: The current market demand for encyclopedias also plays a role in determining the value of the books. While encyclopedias were once considered essential reference resources, their use has declined in recent years due to the widespread availability of online information sources like Wikipedia.
Considering all these factors, the estimated value of the 1959 to 1985 Colliers Encyclopedia Year Books, assuming they are in good condition and complete, could range from approximately $50 to $100 for the entire set. However, it's important to keep in mind that the actual value may vary depending on the specific circumstances of the sale and the buyer's interest. If you are looking to sell the books or obtain a more precise valuation, it may be a good idea to consult a bookseller or appraiser who specializes in rare or collectible books.