Often, the inner workings of something are clearest when it breaks. When it's functioning as expected, the details mesh into a sublime unit of successful cooperation. A big happy result overshadows the individual contributions; a jumbled unsettling result redirects attention to whatever broke.
Perhaps surprisingly, that holds for symbols. To determine what information corresponds to a symbol, consider all the ways to prove that differing symbols are mismatches in some fashion. For a symbol to have value, alternatives to it are to some extent inappropriate and inadequate. Which typical messages are judged "true" when the symbol is in place but judged "false" when other symbols are? Or "false" and "true" respectively, or "false" for either, or "true" for either? And veracity isn't the only message outcome to judge and compare. Within messages otherwise identical, does a symbol communicate relatively greater or lesser specificity, formality, emotionality, neutrality? Subtext is still information, as demonstrated by the difference in the recipient's potential reaction.
Then the divergence in message outcomes is a basis for inferring the information for the new symbol via the indirect route of other symbols, which act as points of reference. The true message "X is a telephone" narrows down the information that X could symbolize. Another true message "X is wireless" eliminates further possibilities. A symbol's information is a synthesis whose parts and connections themselves can be symbolically communicated. Divergence outlines the real boundaries of the synthesis, like how parallax bounds objects' real positions. For instance, "X is a telephone" implies a fairly restrictive range for the mass and volume information included in the synthesis that X symbolizes. All one's prior examples of telephones, being sufficiently alike to X to merit the symbol "telephone", are like lines of sight directed in the metaphorical vicinity of X's synthesis of information. X's particular synthesis of size and price and brand and usability, as judged from messages in which X appears, is different than those prior examples but is nevertheless metaphorically closer than the synthesis symbolized by "sasquatch".
At the extreme, symbols could more or less fail to exhibit divergence. When that happens, the superficiality of symbolism is most clear. Generally, humans are too easily impressed and preoccupied by this occurrence. "What if someone abruptly started using the word 'green' for the perception of the color red?" Given the above discussion of pragmatic symbol divergence, it's not that difficult to guess what would happen. If the person never expressed any messages containing that symbol, the mistaken substitution wouldn't matter since symbols are used in messages. He or she could still reach accurate unexpressed conclusions about colors. However, after communicating a message containing the symbol, the recipients would respond by rapidly pinpointing the divergence. Sender: "I got a wonderful green balloon whose color is as vibrant as my car." Recipient: "But your car is red." Sender: "No, my car is plainly green. Green like the round fake nose on the clown who handed me the balloon." Recipient: "Hmm. It sounds like you're calling 'green' what the rest of us call 'red'."
Moreover, the proposed thought experiment is in reality a quotidian event. Scholars of language evolution have tracked gradual divergence of the elements of language. Words replace or combine. Innovative distinctions emerge and outdated distinctions fade. Separate languages cross-pollinate. Creative experiments, intentional or not, sometimes spread and sometimes die. Many times "incorrect" popular usage tramples correctness over the long run. Old-fashioned yet memorable phrases live on in isolated contexts. Idioms break the usual procedures for interpretation. Throughout these changes, communicators employ diverging symbols constantly. Simply by not introducing or modifying every symbol simultaneously, the messages that either use or explain the modified symbol remain understandable. Symbols are the bridges that symbols cross to reach other symbols.
Symbols are the fiat currency of information. Like local price changes, adjustments to the meaning of a few symbols are healthy responses to outside shifts. Like widespread hyperinflation, too many adjustments to too many symbols are detrimental to comprehending the smallest piece.