This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

adj. Unable of being specified.

"Glamour is the peculiar and elusive characteristic that combines, in unspecified and unspecifiable proportions, the qualities of charisma, style, beauty, desirability, confidence, rarity, and mysteriousness."

specifiable   

unspecifiability