The new version breaks many books on our server - the client accepts title lengths of up to 32 characters and many books we have on our server have titles that are quite log. Now that Spigot limits the title to 16 characters all that books are broken.

If you want to check that the vanilla client accepts books up to 32 characters have a look at MCP ItemEditableBook.java:

public static boolean validBookTagContents(NBTTagCompound p_77828_0_)
{

...

String var1 = p_77828_0_.getString("title");
return var1 != null && var1.length() <= 32 ? p_77828_0_.hasKey("author", 8) : false;

...