:::::Look at it this way: I challenge you to find a source for the resistor color code mnemonic that everyone knows and uses ("bad boys rape our young girls but Violet gives willingly"), but isn't published anywhere you would consider relevant. Yet, there's something notable about an oral tradition that propagates without ever being written down by the practitioners in the field.  As such, it deserves mention in an encyclopedia, even if the only sources that can be found aren't textbooks or technical papers. 
 :::::Just look at the citations in electronic color code#Mnemonics — a book about literature, and a book of fiction! Naturally less-memorable versions will appear in textbooks. For obvious reasons, that mnemonic as well as the acronym TWAT aren't going to be found easily in technical sources. The fact that I found better sources for TWAT than for the resistor color mnemonic surprises me, frankly. =