The data isn’t wrong, but there is a slight issue with the conclusion you can form off it. For example if I were to speak to 1000 people about whether they remembered what they ate today, and 999 of them said yes, I may infer that memory lasts for at minimum half a day. This is clearly inaccurate. Typically this isn’t an issue in research because you only suppose it could be the case and that further investigation is needed to confirm this.
The only problem with this, is why our brains would be more suited to store language. If you consider a short-term memory capacity limit principle, then our brains are not capable of being more suited to store language. If you consider perhaps a short-term memory capacity principle along with particular cases of being more suited to storage, in this case, the simple 7±2 is wrong on its own but right in the dual-system.
In the 1970’s for example, research suggested that there was no such thing as a capacity limit and that instead it was a time limit. More recent research agrees that both of these are present (a time limit and a capacity limit) as a dual system. There is also no precise classification of ‘items’ as it is more so chunks. One may assume that an item is something like ‘3’ but our brain may not represent ‘3’ as a single item, so the exact quantity may not even be anything like what we perceive it to be.
For example in this paper: What are the differences between long-term, short-term, and working memory? (2008)
It is still quite possible that there is a speech-based short-term storage mechanism that is by and large independent of the chunk-based mechanism. In terms of the popular model of Baddeley (2000), the former is the phonological loop and the latter, the episodic buffer. In terms of Cowan (1988, 1995, 1999, 2005), the former is part of activated memory, which may have a time limit due to decay, and the latter is the focus of attention, which is assumed to have a chunk capacity limit.
Later studies suggested that the limit in capacity is more typically only three or four units (Broadbent, 1975; Cowan, 2001).
Or in this paper : George Miller’s Magical Number of Immediate Memory in Retrospect: Observations on the Faltering Progression of Science (2015)
This kind of dual, item-plus-time-limit approach seems to have some validity (e.g., Cowan, Lichty, & Grove, 1990; Chen & Cowan, 2009), though both kinds of limits must be painstakingly disentangled from interference effects (Cowan, Saults, & Blume, 2014; Oberauer, Lewandowsky, Farrell, Jarrold, & Greaves, 2012; Ricker & Cowan, 2014).
The capacity is clearly controversial still, even those at the forefront of the research do not all agree with each-other.
Even this paper(2010)
In a famous paper humorously describing “the magical number seven plus or minus two,” Miller (1956) claimed to be persecuted by an integer. He demonstrated that one can repeat back a list of no more than about seven randomly ordered, meaningful items or chunks (which could be letters, digits, or words). Other research has yielded different results, though. Young adults can recall only 3 or 4 longer verbal chunks, such as idioms or short sentences (Gilchrist, Cowan, & Naveh-Benjamin, 2008). Some have shrugged their shoulders, concluding that the limit “just depends” on details of the memory task. Recent research, however, indicates when and how the limit is predictable.
The recall limit is important because it measures what is termed working memory (Baddeley & Hitch, 1974; Miller, Galanter, & Pribram, 1960), the few temporarily active thoughts. Working memory is used in mental tasks, such as language comprehension (for example, retaining ideas from early in a sentence to be combined with ideas later on), problem solving (in arithmetic, carrying a digit from the ones to the tens column while remembering the numbers), and planning (determining the best order in which to visit the bank, library, and grocery). Many studies indicate that working memory capacity varies among people, predicts individual differences in intellectual ability, and changes across the life span (Cowan, 2005).
It has been difficult to determine the capacity limit of working memory because multiple mechanisms retain information. Considerable research suggests, for example, that one can retain about 2 seconds’ worth of speech through silent rehearsal (Baddeley & Hitch, 1974). Working memory cannot be limited this way alone, though; in running span procedures, only the last 3 to 5 digits can be recalled (less than 2 seconds’ worth). In these procedure, the participant does not know when a list will end and, when it does, must recall several items from the end of the list (Cowan, 2001).
Added to this I have for example made a new method that increases your verbal memory span by a little which I haven’t shared yet. This method works on all verbal data and is very strange. I’m not even sure if it works for everyone yet. It does not use any mnemonics but does use an unusual form of rehearsal and can increase digit span by perhaps 4 digits or more. It does take a little more time without practice. It does however prove that span isn’t very simple.